Political identity is deeply fundamental to people
To some people. Not to all people.
I may be falling victim to the typical mind fallacy here (my identity is not linked to any political group), but the latest Gallup poll says: "Forty-two percent of Americans, on average, identified as political independents in 2013, the highest Gallup has measured since it began conducting interviews by telephone 25 years ago. Meanwhile, Republican identification fell to 25%, the lowest over that time span. At 31%, Democratic identification is unchanged from the last four years but down from 36% in 2008."
The same link shows a graph for declared political affiliation and I it doesn't look likely to me that the shifts in political allegiance are solely due to some cohort dying off and another cohort growing up to be counted in the poll.
Politics as gymnastics for rationalists. No one one Less Wrong is quite sure why politics is a taboo topic or how things got to be that way. What we do think we know is that politics is a great way to bring out the irrationality in people. So why not take advantage of that and use politics as a way to measure rationality? Since politics brings out the most irrationality, it should provide the strongest signal. Since there aren't useful objective metrics of how a political discussion went, we'd have to use subjective judgements by neutral third-party raters, kind of like they do in gymnastics. (In the comment thread for this post, feel free to find fights that you have no dog in, improvise a rationality rubric, and grade participants according to your rubric... let's see how it goes.)
Be a sheep. This is probably the exact opposite of what you were taught in your high school civics class. But if my friend Jane is more intelligent, more informed, and less ideological than I am, it seems like voting however Jane is going to vote is a strict improvement over voting however I would naively. It also saves me time, and gives Jane an incentive to put even more time in to carefully considering political issues since she now controls two votes instead of one. Done on a large scale, this could provide an interesting twist on representative democracy. Imagine a directed graph where each node represents a person and an edge is directed from person A to person B if person A is auto-copying person B's votes. There's a government computer system where you can change the person you're auto-copying votes from at any time or override an auto-copied vote with your own personal guess about what's best for society. Other than that, it's direct democracy... all bills are put before all citizens to vote on. Problems this might solve: