It would encourage more people to pull the 'you don't agree with me politically so therefore I want a second moderator's opinion' card. Which, to be fair, is already allowed.
In general, I believe that a chart of those who believe that the moderators are biased against their politics would match up pretty well against a chart of those with numerous prior warns, having seen people from all aisles of politics using 'moderators biased' rhetoric as an excuse for breaking the rules and being rude. It's bit amazing that this thread seems stuck on this topic though, seeing as both LWDT and RWDT got shut down, which, at least at the face of it (I never ventured into these threads), seems unbiased enough.