Ignore all the joke answers here. It seems insensitive given the subject matter. He’s probably lonely and feeling left out. If he has siblings it’s all the more likely. I was an alienated teenager who was in a place similar to your son I think. I eventually realized I and many others we’re being used to further the agenda of some unsavory fucks who wanted to send us back to the 1860’s. Try to show him how much he means to you. Let him know you care about him. Just don’t drive him away, Show some love and compassion and he’ll realize he’s drinking the kool-aid eventually I think. Hope this helps, good luck!