"Arguments are soldiers" is practically the definition of democracy.
Respectfully, that's not a correct use of the metaphor. The point is that unwillingness to disagree with other positions simply because those positions reach the desired conclusion is evidence of being mindkilled. You don't shoot soldiers on your side, but for those thinking rationally, arguments are not soldiers, so bad ideas should always be challenged.
It would be very easy for new would-be LessWrong readers to see the politics threads, jump to conclusions like "Oh, these people think they're so smart but they're actually a bunch of Blues! A wise Green like me should look elsewhere for rationality." Repeat for a few years and the average LessWrong biases really do start to skew Blue, even bad Blue-associated ideas start going unchallenged, etc.
This is a real risk, but it's worth assessing (and figuring out how to assess) how likely it is to occur.
By "thinking rationally", you must mean epistemically, not instrumentally.
If (to use as Less-Wrong-politically-neutral an allegory as I can) you are vastly outnumbered by citizens who are wondering if maybe those birds were an omen telling us that Jupiter doesn't want heretics thrown to the lions anymore, I agree that the epistemically rational thing to do is point out that we don't have much evidence for the efficacy of augury or the existence of Zeus, but the instrumentally rational thing to do is to smile, nod, and point out that eagles are we...
Summary: I propose we somewhat relax our stance on political speech on Less Wrong.
Related: The mind-killer, Mind-killer
A recent series of posts by a well-meaning troll (example) has caused me to re-examine our "no-politics" norm. I believe there has been some unintentional creep from the original intent of Politics is the Mind-Killer. In that article, Eliezer is arguing that discussions here (actually on Overcoming Bias) should not use examples from politics in discussions that are not about politics, since they distract from the lesson. Note the final paragraph:
So, the original intent was not to ban political speech altogether, but to encourage us to come up with less-charged examples where possible. If the subject you're really talking about is politics, and it relates directly to rationality, then you should be able to post about it without getting downvotes strictly because "politics is the mind-killer".
It could be that this drift is less of a community norm than I perceive, and there are just a few folks (myself included) that have taken the original message too far. If so, consider this a message just to those folks such as myself.
Of course, politics would still be off-topic in the comment threads of most posts. There should probably be a special open thread (or another forum) to which drive-by political activists can be directed, instead of simply saying "We don't talk about politics here".
David_Gerard makes a similar point here (though FWIW, I came up with this title independently).