Ilya Somin over at the Volokh Conspiracy is arguing that political ignorance is rational. This reminds me of a previous post of mine: Interest Universalism (that term is a regretful coinage, but I couldn't come up with anything better).
We all have to chose what to spend our energy on, and it appears that there is a special name for those who chose to spend almost no energy at all on politics: "swing voter". According to a study that he kind of waves his hand at (I spent about twenty minutes trying to tack it down through his links and failed), swing voters have far less political knowledge on average than partisan voters. Since swing voters are pretty much the ones who decide elections, this implies that our elections are decided by the most ignorant.
So regardless of what is rational for the individual, this tendency for many people to ignore politics arguably has a very bad effect on the general welfare. I would tend to make that argument on the grounds that people who know more about politics would tend to vote more like me. I may be wrong about that, but I can't believe that if Republicans during the primaries had known about McCain's policies on illegal immigration, on taxes, on free speech during political campaigns, and on harsh interrogation for terrorists that they would have voted for him. Similarly, I can't believe that if most people really understood the the corrupting effects of earmarks, or the horrors of partial-birth abortion, that they would vote for politicians who support those things.
The behavior of the politicians who support all of those things I named suggests that they agree with me. That's why, for example, McCain avoided talk of illegal immigration during the primaries and became so hostile when others brought up his record on the issue. That's why Democrats get so hostile at groups who want to show pictures of partial-birth abortions. McCain and the pro-abortion crowd agree with me that more knowledge would mean less support for them.