Okay so since topic name is changed, here are my reasons why Karna Duryodhan friendship is highlighted -
Duryodhan's side I guess is justified so about Karna -
Him fighting in the war is good reason why. Firstly, there was nothing in him in the war. He was fighting for two reasons 1) Duryodhan and 2) to Kill Arjun. If Duryodhan would have won the war, he would still be Duryodhan's sidekick. Had he killed Arjun. he would be called slayer of Arjun which is a title he would orgasm over for sure but again, nothing more than that. So he was fighting for supporting his friend and for killing Arjuna, he was ready to let go of all the other Pandavas.
Also, he did not promise he will not capture Yudhishthir, he promised he would not KILL them so he also knew the way to support Duryodhan as well.
I absolutely agree that Krishna and Kunti were just taking turns to come manipulate him, but he was not some Dharmic person to have stuck to so called Dharma. He always did what he wished to. So him not agreeing to go to Pandava side would mean he is loyal to Duryodhana. Now he ofcourse knew Krishna was fooling him about the throne, but he would have been part of the victorious side and also most probably remain alive. So in this case I do hold him in regard for sticking by his friend. He did prove to be a good friend.