Why is rep disabled in General Chat? IMO a lot of people deserve red in politics and religion. A flood of red will surely stop them from giving hate speeches. It's pretty horrible in there.
Because on the other side of it, we don't want people building up their reputation by posting garbage in GC to amuse people, only to have them then use that rep status to attract buyers in BST sections, as though they earned it for being a reputable member worth doing business with. Same reason we don't let people build up iTraders with freebies -- makes things too easy for scammers to look more reputable than they are. And it's not completely disabled afaik. I believe it's just decreased, so those higher rep members can still give pos and neg rep there -- it just gives fewer points. Not sure what the exact numbers are off the top of my head though, and I could be wrong -- might have changed. Hopefully someone else can clarify that part.
As Jenn said, it's not disabled. I received rep in GC recently. But you need to have enough rep power to be able to leave rep.