> If I met a paranoid schizophrenic and decided to spend the next few months building up a relationship with him and confirming all his delusions (yes, you're special with divine powers, yes your family and friends are all spying on you and trying to spiritually weaken you, here's how they're doing it, by the way you have to do whatever it takes to stop them, etc) I would expect to be charged with something if he then went and killed someone.

Assuming you don't attempt to tell them to do something I'm not actually sure you would. The first amendment is pretty strong, but ianal.