Quote Originally Posted by thir View Post
There is the crux of the matter, isn't it? Consent can only be given by relatively normal and informed people. And who are they? Well - most of us! But not all.
But who is to say who aren't?
"Friends don't let friends do bad things." You can't stop a legally competent adult making what looks to you like a really bad mistake, but you can warn them in any way that works, try to make them look at the situation with clearer eyes, maybe show them facts they didn't know. It may not work at the time, but help them later when they start having secod thoughts for themselves.