You might be an extreme centrist. Or an extreme pragmatic. Not all extremists are the "take some idea to its (il)logical conclusion and start blowing things up" type.

Impact of charitable donations is, at least within the domains that most people can give, directly proportional to the size of the donations. It's not at all clear, however, that extremist participation in politics produces a greater impact in the desired direction than casual participation.

I think that in some cases, it probably does, whereas in others it does not.

It probably depends of the decision process you're trying to influence:

• If you're voting for a candidate, you don't have any incentive to vote in a way more extreme than your preferences - with more than two candidates, you can have strategic voting which is often the opposite incentive, i.e. voting for a candidate you like less that has more chances of making it.

• If a bureaucrat is trying to maximize utility by examining people's stated preferences, then you can have an incentive to claim extreme preferences for the reasons Yvain gives.

Informal discussions of what social norms should be look more like the second case.

Elected politicians have to deal with the two systems, on one side they want to take a moderate position to get the maximum number of voters (median voter etc.), on the other hand once elected they have an incentive to claim to be more extreme when negotiating in their constituents' interest.

Could you spell out what you mean by extremist, and how the analogous argument goes?

If there are three candidates, then yes, you should give all your support to one candidate, even if you hate one and don't distinguish between the other two.

But that hardly makes you an extremist. I don't see any reason that this kind of argument says you should support the same party in every election, or for every seat in a particular election, or that you should support that party's position on every issue. Even if you are an extremist and, say, want to pull the country leftward on all issues, it's not obvious whether equal amounts of support (say, money) to a small far-left party will be more effective than to a center-left party. Similarly, if your participation in politics is conversation with people, it's not obvious that always arguing left-wing positions is the most effective way to draw people to the left. It may be that demonstrating a willingness to compromise and consider details may make you more convincing. In fact, I do think the answer is that the main power individuals have in arguing about politics is to shift the Overton window; but I think that is a completely different reason than the charity argument.

and then I looked up your comment on LJ and the comment it replies to and I strongly disagree with your comment. This has nothing to do with the charity argument. Whether this argument is correct is different matter. I think the Overton window is a different phenomenon. I think the argument to take extreme positions to negotiate compromises better applies to politicians than to ordinary people. But their actions are not marginal and so this is clearly different from the charity argument.

Value of information about which political side is more marginally valuable makes unbiased discussion a cause that's potentially more valuable than advocacy for any of the political sides, and charities are similarly on the same scene. So the rule is not "focus on a single element out of each class of activities", the choice isn't limited to any given class of activities. Applied to politics, the rule can be stated only as, "If advocacy of political positions is the most marginally valuable thing you can do, focus on a single side."

There's a standard argument about "efficient charity" that says you should concentrate all your donations on one charity

If this argument was universal, it would be rational to invest in a single stock and the saying about all eggs in one basket would not exist.