During the time of war also, they did not let Karna do war. They always insulted every given chance against Karna. Is it just because Karna is a Sut Putru? Or they just hate him that Karna was a strong warrior and supporter to Duryodhana. Or they believed caste system a lot? Or why?

Is Karna a lesson for every person in Kaliyug to just give and not expect anything? When a great warrior and donor like Karna was not able to get anything for him what he deserved. Even his body was also not cremated on Earth in deed, human in Kaliyug can nowhere match to his sacifices. So is this a lesson to be learnt from his life?