Basically, the contention is that Star-Lord / Peter Quill is the true villain of the piece and his hot-headed nature when they're trying to take down Thanos leads to him breaking free, beating the crap out of everyone, and eventually wiping out half the universe with the help of the Infinity Gauntlet.
Well, this very take was put to Pratt and his response? "Look – the guy watched his mother die, he watched as his father-figure died in his arms, he was forced to kill his own biological father and now has lost the love of his life," argued Pratt in a recent interview with Radio Times. Pratt went on, making the point that his reaction was human and that humanity was in keeping with the spirit of the film and the Guardians of the Galaxy, so it makes sense in that context.
"And also, I blame Thanos, OK? Jeez, how come he's not getting any blame? Clearly I'm very sensitive about this." Look, let's not get our leather pantsuits in a twist over this, Chris Pratt. Star-Lord messed up and caused the whole thing to unfold the way it did.
But, y'know, recent casting announcements kind of undo that ending - so, really, no harm and no foul here. Also, 'Avengers: Infinity War' made a gazillion dollars, so clearly the ending played with audiences.