Various shades of grey?

I recently heard a podcast in which a speaker, formally trained in Hindu spirituality, alleging that we are giving Karna more credit than he deserves. True, fate had not been kind to him. Being a product of an unceremonious, society-unsanctioned union, his mother, Kunti, decided that the best course of action was to abandon him in a vessel by the river, to be taken away by the waves, armed only with grand ornaments on his body.

Karna had so much to offer, but was denied on account of his adopted status. He wanted to achieve many things in his life and yearned for validation. All the disappointments made him an angry man. His attempt at learning sorcery and archery was thwarted by his unknown familial background. For that, he had to lie to be Parasuraman's disciple, and when his bluff was discovered, he paid dearly. Parasuraman then cursed him that he would forget his skills at the most crucial moment of his life. 

Karna was also denied entry into competitions due to his background as a charioteer's son. Only royalties could partake in specific grand competitions. He was humiliated in public when he attended Drupadi's svayaṃvara.

It was only Duryodhana of the Kaurava clan who gave him dignity by providing him with land to rule, thereby elevating his status to that of a kshatriya (ruling class). For that, Karna was eternally grateful.

That incident made Karna forever indebted to the Kaurava clan. He became privy to all their malfeasance. He showed blind, unwavering support to Duryodhana. He not only failed to raise an alarm when Draupadi was disrobed, but also encouraged the Kauravas to do so. He remained on the Kauravas' side, even though he knew their actions were clearly wrong and their tactics were well below the belt. Karna was also the mastermind in tricking and trapping Ahimanyu, Arjuna's teenage son and killing him unceremoniously and not following the rules of engagement. realising their below-the-belt tactics. Even after knowing that the Pandava brothers are his blood brothers, Karna chose not to value that but was still hellbent on killing them.

So was Karna a good or a negative character? Is he a hero, villain or anti-hero?

That is precisely the point. The Mahabharata is not a book that tells stories. Its characters are not one-dimensional; they are complex. Unlike the actors that we encounter on the silver screen, who are either good or bad, people in real life are not. In real life, everyone is inherently good. Life circumstances shape the way they act. I think the Hindu scriptures are not meant to give us direct answers like a mathematical formula. As complicated as life can be, these references only make us put on our thinking caps to individually or as a group argue the merits and demerits of an action and perhaps come up with alternatives.