I think you missed my point. Yeah, they've got a special prison in canon for dark jedi, but my question wasn't whether they are physically capable of holding people force users who haven't broken any laws, it's whether they're permitted to. Touching the dark side all by itself isn't a crime. How would they even prosecute it? And aside from the problems of proving it, a hypothetical dark sider who never harmed anyone is essentially just a religious minority, and you can't throw people in jail for that in a free society. So the prison is for people who go dark and start killing people and so on as a result. Committing other crimes that justify prosecution, after which they can then be imprisoned at the special facility.
Without Cam going nuts and going all dark lord, all the Jedi can do is kick him out. Which would be the last thing they want to do if they're smart, because if you think someone's a dark sider you want to keep as close an eye on them as possible and try to bring them back. Letting them loose would be idiotic.