I don't think that giving appropriate advice is disrespectful of one's right to make decisions. If a friend asks you for tips on how to do something stupid and

I don't think that giving appropriate advice is disrespectful of one's right to make decisions. If a friend asks you for tips on how to do something stupid and self-harming (according to your judgment), it's okay to say "Don't do this" and not help them. Actually, that might be the best thing you can do for them.