Right on! In my experience, just showing them what the functional impairment due to BP has done over the years, the missed and messed-up chances, the effort put in compared to the things you achieved, it far more convincing than to keep making the point that mental illness, BP, a mental disorder is real. Admitting there is a problem is at least a first step towards acceptance. And some people just don't like the labels or psychiatry. I can relate to that viewpoint certainly to a rather large extent. Heck, we often don't like them or really believe in them.

A good, similar, approach might also be to not emphasise your own opinion on the matter but just state the fact that you receive treatment, got diagnosed, and that they do that for a reason.