The thing about slavery though is the earlier you get it the more powerful it's going to be. When you leverage your production with slavery in the early game you can rapidly speed the expansion phase of the game. The sooner you get your economy set up early in the game, the faster you're going to grow, and I believe giving this sort of advantage to only one of the civs in a particular game is imbalancing.
I don't mind religion specific bonuses, it adds more character to the game. However slavery is a very important game mechanic that can drastically alter a civilization's means to expand early, or quickly produce an assault/defence force. It is in my opinion a tool that should be available to either everyone or no one at all.
Anyway, i was more posting this for my own selfish venting purposes. I doubt I'm going to change anyones mind. I'll just have to accept the fact I need to adopt OO every single game. Hurray