There's an unfortunate irony in the fact that Peter Quill, a.k.a. Star-Lord, frontman of the Guardians of the Galaxy and one of the coolest heroes in all of the MCU has become one of its most disliked, but for many fans, there is just no overlooking his actions in Avengers: Infinity War - actions which had five years of direct consequences and a lifetime of fallout.
The infamous moment that soured fans was when he decided to repeatedly punch Thanos just seconds before the Avengers removed the Infinity Gauntlet from his hand, reawakening the beast and preventing them from doing so. That decision eventually led to the snap that dusted half of the universe, Quill included.
Yes, Peter was grieving the loss of Gamora and wanted to take his frustrations out on the being responsible, but his actions caused billions of people (and beings) five years of their lives. That's not even taking into account the important moments that those who were blipped missed out on, the lives that were changed, and all of the damage done by that stupid decision.
The movies sidestepped any kind of reflective moment from Peter because he too was impacted by his poor decisionmaking, but fans have struggled to let it go. Sure, he is still a beloved member of the Guardians of the Galaxy franchise and we're eager to see how he returns, but he definitely lost a lot of respect for unwittingly allowing Thanos to execute his dastardly plan.