Matt Yglesias has a post up where he says:

I tried to explicitly say that I didn't want the story to be read as an analogy since I don't believe in trying to conduct arguments by analogy.

Analogies are sketchy, though useful when used well. There are two primary issues I think. First, analogies are a precise phenomenon, not a willy-nilly appeal to ad hoc affinities as they are used in many contexts. For example, people actually need to know something about one of the elements to obtain more insight about the other element. That is, you need to know something about the source to map information onto the target. So, for example, the analogy between Catholics:Protestant and Shia:Sunni is close useless because most people don't even have a detailed knowledge of Christianity and the differences between Catholicism and Protestantism to translate that structure to the case of Islam. Secondly, widespread recourse to analogies tends to breed sloppy thinking because of their imprecision. Analogies are good for "quick & dirty," but nothing really beats sharing a common base of data with those whom you are attempting to communicate with.