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.