Mr. Spak:
Teaching these people things is like teaching someone to not be straight. The brain is wired a certain way and anything incompatible with it will just bounce off.
There are former Christians, as well as moderates on the board, who would argue you took the right approach -- except for your having deliberately humiliated the man in front of your mutual co-workers, which you did -- in attempting to educate your coworker. They themselves were freed of fundamentalism through education.
Several younger members of the Westboro Baptist Church, for example, ended up leaving because they recognise their actions were wrong. And one member in particular left because she lost an argument and said as much after she also left.
I had some interactions with a fundie at work - I had the advantage that he had some kind of engineering degree, so he couldn't just dumb redneck his way out of understanding me. In addition, the audience for our, um, interactions were also technically knowledgable.
He knew I kicked his ass right out of his mouth in the observable reality sense, but he still had no notion that he might be wrong.
It's never safe for someone publicly humiliatd to tell the one who did it, "Well, I was totally wrong about some of my foundational beliefs. Thanks for embarrassing me until I saw the light."
Would you do that and risk more mockery?
Again, you'll never agree with my beliefs and I have little reason to argue with you about them; I do not believe atheism endangers the soul. There's no urgency whatsoever in attempting to prove my claim. Suffice it to say, however, that I did not pull this claim out of my ass. I believe it, and I have reason to.
If I am right that (a) "God" - something ancient, intelligent, and interested enough in our evolution to fuck with it from time to time, exists; and (b) it's that god and not some other, then this being in which I believe doesn't need our slavering adulation or constant praise.
It wants us to treat each other without cruelty or utter malice. Our minds and our very substance can be marred beyond any hope of complete repair depending on just how badly we befoul our own world and our fellow human beings.