Ian,
Here in Finland we celebrate Mothers' Day to day, so I'm might be biased.
But I do think, that one should not divorce one's parents just for the sake of "autonomy" (btw, you should check his interpretation of the word autonomy!).
However, I do think, that for the sake of our peace of mind and balance therein we should divorce from everybody causing us pain and tumultuous (negatively) thoughts in general, because those feelings tend to stand in the way of not only autonomy, but the very well being of a person.
So yes, divorce your brother and be your own man.
Ritva