I was confused reading most of your post until I realized you're talking about furries but I am still confused about what you mean by "what they're into" or "group on youtube" or what a mutual is. A mutual friend maybe?
What other people do is beyond your control. All you can do is control how you handle something that you dislike. If something someone else does goes against your beliefs, morals, or values, then it's in your best interest to disassociate with those individuals. As for friends hanging around with bad influences, I wouldn't suggest unfriending them, but let them know what you think and accept their reply for what its worth. They might have their reasons for befriending someone you dislike, but they should respect that you don't want those people being around you or being brought up in your discussions.
Life is full of douchbags, it's the way things are. Don't let yourself stress over someone else who is too inept to be socialable. Life is too short worrying about people not worth worrying about.
