I mean the comic later adopts it for ACT 6 and post-canon but the idea that Gamzee is a no nuance murder clown who was always a bad guy. A lot of things contribute to why he lost it and got suckered in to following the script he was given by Doc Scratch, namely looking into the possessed Cal's eyes. This doesn't mean the things he did can be completely excused, there are just reasons for them that aren't being straight up evil.

My specific interpretation, at least of his earlier depiction before he became more of a tool to move the narrative along, is that he was suckered into believing he had a destiny to follow after his entire belief system and single coping mechanism were snatched away from him.

"My goat dad's gone, my entire life has been a lie, my friends don't really care much about me (until i lash out and kill people), what's that? none of this is real and i'm the chosen one all i gotta do is kill my friends? you know wht hell yeah brother i love you cal mwa mwuwum wmwa"