Charles:
Yes, analogy is limited.
I don't know about fascists using this analogy more than progressives. Marx compared his method in Capital to natural history.
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The analogy is more than limited, Charles, it is really vicious. The whole reactionary tradition in political theory has been grounded in organic views of the state, beginning with Plato's _Republic_. If your eye offend you, pluck it out. Perhaps good for an organism, vicious for a state.
To compare two methods is _not_ to compare the objects of the two studies. The comparison of the body politic to the organic body is inherently anti-revolutionary. Humans _make_ their history in a way that does not remotely resemble the way in which a a fetus makes itself into an adult organism.
It is important to use care in the choice of metaphors -- and to keep separate what a metaphor does and what an analogy does.
Carrol