I wonder if it is not so much a person's beliefs that people have difficulty in separating from the person (and I agree, by the way, that a person's beliefs will affect a person's outlook on life and their approach to it), but the fact that to a person of faith, the faith (whatever it is), or the possession of faith is very important to them, precious even, so that when they think someone is attacking precepts of that faith the person feels, as it were, wounded. I can understand that.
Turn that statement around and it can apply to people of no faith as well.
And of course RD would be polite if any of us met him. Unless we were threatening him physically or hurling abuse at him, why wouldn't he be? 