I don't have a problem with such libs either, but I'm not aware of any such liberals on FR. Plenty of libertarians fit that description, but the only liberal I know of here is MurryMom and she certainly does not discuss anything with thoughtfulness or courtesy.
I had a run-in with a CINO a few days ago, a sloganeer with no wish for thoughtful debate or the skills either. It wasn't long I was thrown the typical "you're a Klansman" response.
So yeah, they're about....
Well...one that comes to mind off the top of my head is Liberallarry. While I certainly don't agree with his positions, I've never encountered any of the vitriol that I have seen with others. Another one may be Logsoul...only because he seems to take contradictory positions on just about everything. He was a big Plame defender...and while I had a long, heated debate with him, he stood by his position without resorting to namecalling. Thankfully, the abusive ones don't last long.