I understand that, but I still think the same thing applies. Once you go in, you're not coming out. The real question is, will this actually help him, or will it hurt him? I imagine they're going to be taking a lot of his freedom away as well as the majority of his tugboat. When he realizes he can't buy as many toys as he used to be able to, can't use the internet as much as he used to be able to if at all, and if they do, he'll likely be monitored or have some kind of parental controls, I can't imagine that going over well, not to mention the fact that he'll be stuck with a bunch of slow-in-the-minds that he doesn't care for and elderly people. What's going to happen when they realize they can't control him? They can't release him back to anyone, so the only option is to ship him off to some facility and keep him controlled via drugs. But to bring this back to the group home, he's not like the others there who don't realize they're fucked or old enough to not give a shit. He's intelligent enough to be completely aware that he just lost all of his freedom.
Just like the fear of hurting Barb(or fear of legal consequences) made him pull his punches or even fake them, I'm pretty sure the fear of going to prison would stop him from committing arson and murder. Either way, this is an extreme case. No troll has ever fucked with Chris in this way, and he's been showing that he can be easily manipulated since the very first troll.
I think we need to keep in mind that anyone who tries to trick Chris into committing a crime is also going to be liable for the crime. If he ever goes on a killing spree and it turns out to be because some psychopath put him up to it, I guarantee you that the psychopath is going to prison as well. Maybe I'm just being optimistic, but I don't think anyone could convince Chris to actually kill someone or himself. Anyways, the fear of they themselves going to prison is a good deterrent for something huge like trying to trick someone into committing murder. Now, if Sonichu himself starts telling him to do crazy shit without being puppetted by psychopaths, that's when he needs to be locked up.