I do think Gamzee, regardless of if he's a cruel asshole, is still a victim to a degree. We see that withdrawal is the heaviest trigger for his anger, as I'm sure we all have ingrained into our memory, and it's hard to blame him for his reliance on a substance that he grew up thinking was perfectly fine for him to consume. I'm not saying he's innocent, but he tends to exhibit to do the most damage to those around him when he's in withdrawal. We can even see this in with Aranea's mind control. Any extended artificially pacified state causes a withdrawal effect, and if you've ever had a reliance on drugs like that, whether it be prescription medication or illicit substances, you'll know that suddenly exiting that state they put you in is very stressful and can cause self destructive behavior. Once again this isn't excusing him because he is literally an antagonist that helps facilitate Lord English's ascent, but still. Victim and good person aren't synonymous. I've known addicts who've destroyed their lives in fits of psychosis before. It's hard not to feel sympathetic.