How can I help a friend who is falling into "witchcraft"?

I have this friend, N, that has recently started believing things very out of the ordinary. He said that he's been getting into paganism and studying runes and candles. I told him that was very interesting, it sounded like a fun time and a good hobby to have. N let me know that it wasn't just a hobby, but that it had a function and purpose, a sort of witchcraft.

I come from an academic background; it doesn't seem healthy to me to actually believe and try to practice witchcraft, not because it might be real, but because of the mental health associations with it. So I told my concerns to N but he brushed them off, saying that people have the right to believe in what they want. I respect that, but I do not want N to fall into delusion. I let him know, as respectful as I could, that believing in witchcraft does not make it real and that it wasn't healthy to believe otherwise. He got really bothered when I told him he should talk to his therapist about this stuff. N has a history of mental health issues and was in a deeply abusive relationship for a few years which cause him a lot of grief. I was accused of being rude and trying to impose my beliefs. His last message to me was him asking me to stop and that anyone has a right to believe what they want.

I cherish N a lot as a friend, I do not wish them any harm. I respect that anyone has a right to believe what they want, but I really don't think this is healthy for my friend. Is there any way I can help him? Is the best way forward to just stop and let him be?