Slurs have power because of how they’re used and what it evokes when someone says them. Not because groups have decided to be offended by them. Target groups don’t give slurs power; the weight of historical and current use gives them power.
Words mean things.
The n-word is a slur because it has always been used to say that black people aren’t really human and to incite violence. That is what that word means when it’s said by someone who isn’t black. You can’t say that word as a nonblack person without invoking that meaning to some extent or other, even if you don’t mean to. That’s not a meaning black people give the word. That’s a meaning that white people created.
Likewise the r-word, especially in noun form. (It’s not always a slur in adjective form, but it always evokes the slur a bit, so it’s better to use a different word if you can). It’s a slur because what it means is someone who isn’t really a whole person because their brain doesn’t work right. That’s not a meaning folks with disabilities are imagining in order to feel offended, and it’s not a meaning they can get away from by deciding not to be offended.
Calling someone a slur means something. It’s a threat. And an implied threat to other people in that group.
Other people can feel how they want about it, but how they feel won’t erase the fact that someone saying a slur is making a threat. Feelings don’t erase violence and threats of violence.