I would stop them at all costs. There's no such thing as karma, but if there were wtf does that have to do with anything?

I think it would have to be a child or someone like a close sibling that you have had some kind of connection with to even have a prayer of dissuading them. Such is the strength of the madness you speak of.

I would only intervene through advice. I separated myself from all things religious and they have condemned me and they wouldn't think twice if God punished me by taking me off the earth. I'm not stressing over religion anymore. Not even with family.