Evil is cool. It can be a lot of fun to keep people on their toes - or even freak them out a bit. And it's okay even. If there's a lesson to be learned and they'll look back on it as good fun, then go ahead and try on the "evil hypnotist" costume. It's just that doing the evil hypnotist thing for real is almost always a bad idea.
I'm not going to waste time moralizing that "you shouldn't be evil because it's morally wrong", because that's completely unpersuasive. Either you agree or you don't care. Well, mostly. I could try to use dark arts to moralize you, but light arts tend to work better. That's kinda the point of this post.