It would appear that there is exactly one Christian Left community on livejournal, and it has very, very few members and only three or four posts, all by the same guy. The last one was posted just before Terry Schiavo died. I admit I didn't look at the comments. (Oh, I just found another, about liberal Christianity. Also not very active.)
There are half a dozen, at least, Christians on my list whom I would describe as liberal to varying degrees, and who describe themselves as such. So, tell me: if I started such a community, would you join it? This question is by no means limited to Christians, btw. I would set it up so I approved membership, thereby giving myself the right to kick people out if necessary, but I'd let in everyone who went to the trouble of asking, and the rule would be the same as the rule here: reasoned, friendly debate.