You're exactly right. It has the net effect of preaching to the choir, convincing noone that wasn't alread convinced. Anyone that may have been swayed by a mature discussion and rational exchange is driven away.
I'm not concerned that anyone would be "swayed" by hearing a liberal's take on a subject.
I'm so convinced that the Conservative interpretation is the true one that I believe that Sean can hold his own by by polite and simply staying focused without the ad hominem attacks.