How to discourage my younger cousin from joining a cult?

My younger cousin started hanging out with this group of hippies at his school. I don't even think they are hippies, but they look like it and they seem to be into that style of clothing with the peace symbol, etc.. One of his new friends wheres a t-shirt that says meat is murder,which is crazy. I don't know what my cousin's whole obsession is with this vegan cult because I think it is so extreme. All I know is that he has been very withdrawn since he started hanging around this new group of people. He has also made it unbarrable to have dinner with as he goes on and on about how eating meat is murder and people who eat meat are no different than slave masters. I can't deal with this, but at the same time, nothing I say influences him away from this whole cult thing he has got involved in. Any suggestions on how to get him back on the right track?