As a Christian, I would also forgive my son of this, or pretty much anything else. We've all fucked up. I've been forgiven so I should forgive.

However, forgiving someone doesn't mean that I'm going to allow that person to harm myself and my family. You still have to take who they are as a person into your decision making process.

Do whatever you can to help him out of the brainwashing. Armchair quarterback moment, but this needed to be handled way earlier in life.