In my scenario the gym isn't causing actual harm - it's just forcing users to use it in a manner that they consider inefficient - this is the same as the actual extension we're talking about. You can manually unfollow everyone through facebook's UI - but it is cumbersome and difficult.

I think there are some really strong reasons why facebook actually does cause actual harm and I'm not certain why you're being so defensive over that point - but my argument doesn't even involve facebook "causing harm" - it's just involves them having a terrible UX.