No, I think the real problem is that talking about politics brings out the worst in people who disagree with you (because you make them feel angry), and the only the mildly unsavory in people who don't (because you make them feel smug). How many people responded to
What You Can't Say with some form of "Yes for thee, but not for me"?
Telling people an important part of their opinion-forming mechanism -- their facts, or their fact-finding, or their ability to tell "probative" from "normative" -- is just as special case that gives everyone an equal opportunity to show his ass.
I actually spent some time thinking about how you could do better than what's out there now -- provide a way to enforce good rhetorical behavior; set some rules about evidence; and especially, make prominence based on credibility or evidentiary support.
But in the end, I don't think many forum users would really prefer the hard work of keeping their opinions in line with all the available facts to the satisfaction of beating a disembodied un-person in a non-argument. And also, there are a lot of factors working against you:
http://www.singinst.org/Biases.pdf
http://overcomingbias.com