Well, there is the aesthetic appreciation of polemic for its own sake, but that's not going to make you more rational.

I think the most obvious answer, though, is that it can inure you a bit to connotative sneers. Aversion to this kind of insult is likely one of the major things keeping you from absorbing novel information!

One way to do this very quickly - you shouldn't, of course, select your politics for such trivial advantages, but if you do, take advantage of it - is to become evil yourself, relative to the majority's values. There are certain groups an attack upon which constitutes an applause line in the mainstream. If you identify as a communist or fascist or Islamist or other Designated Antagonist Group, you can either take the (obviously epistemically disastrous) route of only reading your comrades, or you can keep relying on mainstream institutional sources of information that insult you, and thereby thicken your skin. (Empirical prediction: hard {left|right}ists are more likely to read mainstream {conservatives|liberals} than are mainstream {liberals|conservatives}.)

(An alternate strategy this suggests, if your beliefs are, alas, pedestrian, is to "identify" with some completely ridiculous normative outlook, like negative utilitarianism or something. Let everyone's viewpoint offend you until "this viewpoint offends!" no longer functions as a curiosity stopper.)