The assumption that someone who left the Mormon church and is upset is completely unreliable because of their anger is silly to me. **Anger does not immediately equal mental problems.**
I left the Jehovah's Witnesses years before I became Mormon, and they attempt to do the same thing with anyone who dares speak out against them. Just a few months ago, they actually referred to anyone who leaves the JWs and speaks against them as "mentally diseased"!
Scientology refers to people who speak against them as "suppressive persons" and treat them the same way.
It's a classic move, also used all the time in politics. Don't address the person's criticism, just attack their character. It's rude, unfair, and doesn't make a lot of sense.