At some point in a person's "training" as a rationalist, there comes a time when they are supposed to be ready to undertake controversial conversation topics without spontaneous combustion of their discussions. (Never mind that jokes and art are not exactly examples of controversial topics...) Rationality encompasses skills such as being able to accurately understand people's motives without caricaturing them, maintaining a good relationship with your conversation partners so that the channels for agreement and the channels for social relations don't get mixed (so that you can disagree sanely with someone), not straying the conversation away from collective truth-seeking and towards mini-wars etc. In fact I would say that a controversial topic such as politics is the best test of a person's actual wisdom and reasonableness.

I understand why some topics may not be appropriate for less-than-rational individuals. (But, again, these topics do not include humour and art and music! Otherwise you should pay a visit to the Wizard of Oz for him to give you a heart...) Anyone who has some legitimate claim towards better rationality skills, however, should at least try to test those better rationality skills on a higher difficulty setting. To forbid anything but sterile mathy discussions about game theory dilemmas involving alien intelligences does not improve the rationality level of people. (This honestly looks to me like cocooning; like fear of the outside world.) Nor does responsibly endeavouring to step into the arena of debates on topics relevant to humanity at large suddenly awaken your primal urges to kill, maim, and enslave your opponents. Ordinary people sometimes discuss this, in meatspace and on the internet. Ideas are expressed, values are clashed (instead of swords, mayhaps), insults are exchanged, people are warned or banned or not invited to the next dinner party. Egad, minds are sometimes even changed. With LessWrong, with all of our claims to an ardent dedication to rationality, I'm expecting to see less of the bad stuff and more of the good stuff. Much more.

Politics is the Mindkiller is not a law of nature, but a word of caution.