Proving yet again you can't argue with extremists. They're gonna have their way no matter what you say.
I usually handle them in the same way I would a know-it-all relative: simply let their words float peacefully through your brain: in through one ear, out through the other. Let all you hear be 'blah blah blah'.
After all, you'll never be able to change their mind, and them yours.
Her phrase ' Let me make one thing perfectly clear:....' should have been the warning sign for him to recognize where things were heading.
Anger and bitterness can make you paranoid, seeing enemies where there weren't any to begin with. It sure can create enemies though, as even the nicest person can only be pushed so far.