I'm with you. It's a cop out so they don't have to explain how someone becomes an x-Christian, especially for the "once saved always saved" flavor sects.
And whenever a Christian like Anders Brevik does something really messed up, they will automatically say "Oh no, he's not a true Christian"
Oy vey, you are opening a mean can of worms when you start to touch on the topic of Christianity and mental illness.
Well not to say that they are all completely insane lol. But Christianity certainly does influence a lot of corruption. And when they write off this as "well those are not true Christians", its sort of like inaccurately saying that Christians are perfect or superior and could never do wrong.