From the sounds of it, I'd have banned you too, especially since you weren't a main and you died before the teammates in the back.
That being said, you have a really crappy attitude in here. Coming in here, demanding an apology, and saying you have no intention of dying while following the rules... well too bad. Losing and dying is a part of the game, and had you stayed with the team maybe you'd have been the catalyst they needed to get to the safe room. Being an admin in L4D2 certainly isn't easy, and they're not going to issue arbitrary bans for no reason.
Your sarcasm will not get you anywhere either. As far as not giving you a chance to talk, I'd prefer the admins ban people and bring it to the forums. That type of discussion in game just serves as a distraction for the 18 other players in there and will hinder their ability to enjoy the game.
Saying you didn't get any kind of hearing does nothing for me. This is not a democracy, we're not elected by anybody, we're not paid. We volunteer OUR TIME to maintain this community and the servers.
I'm closing this. Ban was justified, your post does nothing to help your case.