As KaranM says read the MB as it is and dont use modern adjectives.
Arjuna is reminded by Krishna of the atrocities that Karna had a role in and unleashes the arrow that kills Karna.
"Sanjaya said, 'Then Vasudeva, stationed on the car, addressed Karna, saying, "By good luck it is, O son of Radha, that thou rememberest virtue! It is generally seen that they that are mean, when they sink into distress, rail at Providence but never at their own misdeeds. Thyself and Suyodhana and Duhshasana and Shakuni, the son of Subala, had caused Draupadi, clad in a single piece of raiment, to be brought into the midst of the assembly. On that occasion, O Karna, this virtue of thine did not manifest itself. When at the assembly Shakuni, an adept in dice, vanquished Kunti's son Yudhishthira who was unacquainted with it, whither had this virtue of thine gone? When the Kuru king (Duryodhana), acting under thy counsels, treated Bhimasena in that way with the aid of snakes and poisoned food, whither had this virtue of thine then gone? When the period of exile into the woods was over as also the thirteenth year, thou didst not make over to the Pandavas their kingdom. Whither had this virtue of thine then gone? Thou didst set fire to the house of lac at Varanavata for burning to death the sleeping Pandavas. Whither then, O son of Radha, had this virtue of thine gone? Thou laughedest at Krishna while she stood in the midst of the assembly, scantily dressed because in her season and obedient to Duhshasana's will, whither, then, O Karna, had this virtue of thine gone? When from the apartment reserved for the females innocent Krishna was dragged, thou didst not interfere. Whither, O son of Radha, had this virtue of thine gone? Thyself addressing the princess Draupadi, that lady whose tread is as dignified as that of the elephant, in these words, viz., 'The Pandavas, O Krishna, are lost. They have sunk into eternal hell. Do thou choose another husband!' thou lookedest on the scene with delight. Whither then, O Karna, had this virtue of thine gone? Covetous of kingdom and relying on the ruler of the Gandharvas, thou summonedest the Pandavas (to a match of dice). Whither then had this virtue of thine gone? When many mighty car-warriors, encompassing the boy Abhimanyu in battle, slew him, whither had this virtue of thine then gone? If this virtue that thou now invokest was nowhere on those occasions, what is the use then of parching thy palate now, by uttering that word? Thou art now for the practice of virtue, O Suta, but thou shalt not escape with life. Like Nala who was defeated by Pushkara with the aid of dice but who regained his kingdom by prowess, the Pandavas, who are free from cupidity, will recover their kingdom by the prowess of their arms, aided with all their friends. Having slain in battle their powerful foes, they, with the Somakas, will recover their kingdom. The Dhartarashtras will meet with destruction at the hands of those lions among men (viz., the sons of Pandu), that are always protected by virtue!'"
"Sanjaya continued, 'Thus addressed, O Bharata, by Vasudeva, Karna hung down his head in shame and gave no answer. With lips quivering in rage, he raised his bow, O Bharata, and, being endued with great energy and prowess, he continued to fight with Partha. Then Vasudeva, addressing Phalguna, that bull among men, said, "O thou of great might, piercing Karna with a celestial weapon, throw him down." Thus addressed by the holy one, Arjuna became filled with rage. Indeed, remembering the incidents alluded to by Krishna, Dhananjaya blazed up with fury. Then, O king, blazing flames of fire seemed to emanate from all the pores of the angry Partha's body. The sight seemed to be exceedingly wonderful. Beholding it, Karna, invoking the brahmastra, showered his shafts upon Dhananjaya, and once more made an effort to extricate his car. Partha also, by the aid of the brahmastra, poured arrowy downpours upon Karna. Baffling with his own weapon the weapon of his foe, the son of Pandu continued to strike him. The son of Kunti then, aiming at Karna sped another favourite weapon of his that was inspired with the energy of Agni. Sped by Arjuna, that weapon blazed up with its own energy. Karna, however, quenched that conflagration with the Varuna weapon. The Suta's son also, by the clouds he created, caused all the points of the compass to be shrouded with a darkness such as may be seen on a rainy day. The son of Pandu, endued with great energy, fearlessly dispelled those clouds by means of the Vayavya weapon in the very sight of Karna. The Suta's son then, for slaying the son of Pandu, took up a terrible arrow blazing like fire. When that adored shaft was fixed on the bow-string, the earth, O king, trembled with her mountains and waters and forests. Violent winds began to blow, bearing hard pebbles. All the points of the compass became enveloped with dust. Wails of grief, O Bharata, arose among the gods in the welkin. Beholding that shaft aimed by the Suta's son, O sire, the Pandavas, with cheerless hearts, gave themselves up to great sorrow. That shaft of keen point and endued with the effulgence of Sakra's thunder, sped from Karna's arms, fell upon Dhananjaya's chest and penetrated it like a mighty snake penetrating an ant-hill. That grinder of foes, viz., the high-souled Vibhatsu, thus deeply pierced in that encounter, began to reel. His grasp became loosened, at which his bow Gandiva dropped from his hand. He trembled like the prince of mountains in an earthquake. Availing himself of that opportunity, the mighty car-warrior Vrisha, desirous of extricating his car-wheel that had been swallowed up by the earth, jumped down from his vehicle. Seizing the wheel with his two arms he endeavoured to drag it up, but though possessed of great strength, he failed in his efforts, as destiny would have it. Meanwhile the diadem-decked and high-souled Arjuna, recovering his senses, took up a shaft, fatal as the rod of Death, and called anjalika. Then Vasudeva, addressing Partha, said, "Cut off with thy arrow the head of this enemy of thine, viz., Vrisha, before he succeeds in getting upon his car." Applauding those words of the lord Vasudeva, and while the wheel of his enemy was still sunk, the mighty car-warrior Arjuna took up a razor-headed arrow of blazing effulgence and struck the standard (of Karna) bearing the elephant's rope and bright as the spotless sun. That standard bearing the device of the costly elephant's rope, was adorned with gold and pearls and gems and diamonds, and forged with care by foremost of artists excelling in knowledge, and possessed of great beauty, and variegated with pure gold. That standard always used to fill thy troops with high courage and the enemy with fear. Its form commanded applause. Celebrated over the whole world, it resembled the sun in splendour. Indeed, its effulgence was like that of fire or the sun or the moon. The diadem-decked Arjuna, with that razor-headed shaft, exceedingly sharp, equipped with wings of gold, possessed of the splendour of fire when fed with libations of clarified butter, and blazing with beauty, cut off that standard of Adhiratha's son, that great car-warrior. With that standard, as it fell, the fame, pride, hope of victory, and everything dear, as also the hearts of the Kurus, fell, and loud wails of "Oh!" and "Alas!" arose (from the Kuru army). Beholding that standard cut off and thrown down by that hero of Kuru's race possessed of great lightness of hand, thy troops, O Bharata, were no longer hopeful of Karna's victory. Hastening then for Karna's destruction, Partha took out from his quiver an excellent Anjalika weapon that resembled the thunder of Indra or the rod of fire and that was possessed of the effulgence of the thousand-rayed Sun. Capable of penetrating the very vitals, besmeared with blood and flesh, resembling fire or the sun, made of costly materials, destructive of men, steeds, and elephants, of straight course and fierce impetuosity, it measured three cubits and six feet. Endued with the force of the thousand-eyed Indra's thunder, irresistible as Rakshasas in the night, resembling Pinaka or Narayana's discus, it was exceedingly terrible and destructive of all living creatures. Partha cheerfully took up that great weapon, in the shape of an arrow, which could not be resisted by the very gods, that high-souled being which was always adored by the son of Pandu, and which was capable of vanquishing the very gods and the Asuras. Beholding that shaft grasped by Partha in that battle, the entire universe shook with its mobile and immobile creatures. Indeed, seeing that weapon raised (for being sped) in that dreadful battle, the Rishis loudly cried out, "Peace be to the universe!" The wielder of Gandiva then fixed on his bow that unrivalled arrow, uniting it with a high and mighty weapon. Drawing his bow Gandiva, he quickly said, "Let this shaft of mine be like a mighty weapon capable of quickly destroying the body and heart of my enemy, if I have ever practised ascetic austerities, gratified my superiors, and listened to the counsels of well-wishers. Let this shaft, worshipped by me and possessed of great sharpness, slay my enemy Karna by that Truth." Having said these words Dhananjaya let off that terrible shaft for the destruction of Karna, that arrow fierce and efficacious as a rite prescribed in the Atharvan of Angiras, blazing with effulgence, and incapable of being endured by Death himself in battle. And the diadem-decked Partha, desirous of slaying Karna, with great cheerfulness, said, "Let this shaft conduce to my victory. Shot by me, let this arrow possessed of the splendour of fire or the sun take Karna to the presence of Yama." Saying these words, Arjuna, decked with diadem and garlands, cherishing feelings of hostility towards Karna and desirous of slaying him, cheerfully struck his foe with that foremost of shafts which was possessed of the splendour of the sun or the moon and capable of bestowing victory. Thus sped by that mighty warrior, that shaft endued with the energy of the sun caused all the points of the compass to blaze up with light. With that weapon Arjuna struck off his enemy's head like Indra striking off the head of Vritra with his thunder. Indeed, O king, with that excellent Anjalika weapon inspired with mantras into a mighty weapon, the son of Indra cut off the head of Vaikartana in the afternoon. Thus cut off with that Anjalika, the trunk of Karna fell down on the earth. The head also of that commander of the (Kaurava) army, endued with splendour equal to that of the risen sun and resembling the meridian sun of autumn, fell down on the earth like the sun of bloody disc dropped down from the Asta hills. Indeed, that head abandoned with great unwillingness the body, exceedingly beautiful and always nursed in luxury, of Karna of noble deeds, like an owner abandoning with great unwillingness his commodious mansion filled with great wealth. Cut off with Arjuna's arrow, and deprived of life, the tall trunk of Karna endued with great splendour, with blood issuing from every wound, fell down like the thunder-riven summit of a mountain of red chalk with crimson streams running down its sides after a shower. Then from that body of the fallen Karna a light passing through the welkin penetrated the sun. This wonderful sight, O king, was beheld by the human warriors after the fall of Karna. Then the Pandavas, beholding Karna slain by Phalguna, loudly blew their conchs. Similarly, Krishna and Dhananjaya also, filled with delight, and losing no time, blew their conchs. The Somakas beholding Karna slain and lying on the field, were filled with joy and uttered loud shouts with the other troops (of the Pandava army). In great delight they blew their trumpets and waved their arms and garments. All the warriors, O king, approaching Partha, began to applaud him joyfully. Others, possessed of might, danced, embracing each other, and uttering loud shouts, said, "By good luck, Karna hath been stretched on the earth and mangled with arrows." Indeed, the severed head of Karna looked beautiful like a mountain summit loosened by a tempest, or a quenched fire after the sacrifice is over, or the image of the sun after it has reached the Asta hills. The Karna-sun, with arrows for its rays, after having scorched the hostile army, was at last caused to be set by the mighty Arjuna-time. As the Sun, while proceeding towards the Asta hills, retires taking away with him all his rays, even so that shaft (of Arjuna) passed out, taking with it Karna's life breaths. The death hour of the Suta's son, O sire, was the afternoon of that day. Cut off with the Anjalika weapon in that battle, the head of Karna fell down along with his body. Indeed, that arrow of Arjuna, in the very sight of the Kaurava troops, quickly took away the head and the body of Karna. Beholding the heroic Karna thrown down stretched on the earth, pierced with arrows and bathed in blood, the king of the Madras, went away on that car deprived of its standard. After the fall of Karna, the Kauravas, deeply pierced with shafts in that battle, and afflicted with fear, fled away from the field, frequently casting their eyes on that lofty standard of Arjuna that blazed with splendour. The beautiful head, graced with a face that resembled a lotus of a 1,000 petals, of Karna whose feats were like those of the thousand-eyed Indra, fell down on the earth like the thousand-rayed sun as he looks at the close of day.'"
venug, The story of Krishna seeking alms form Karna is a movie interpolation.
Dhritrashtra and Duryodhana ran the kingdom. Period. Vidur merely advised. Some of his advice was accepted, some were not. 
. I did want to take you up on something you said in another thread, though. You mentioned that the Draupadi disrobing incident may not have been in the Vyasa Bharata at all. Did I get that right? Does this mean that in the chapter and section which describes the dice game and the aftermath, there is no mention of the attempted disrobing? How come no acharya has pointed this out before, if that is the case? This is a question, not necessarily a challenge.