Got any better choices? Same reason why I support Putin. He is not perfect, but in comparison to others - he is a genius.
Ahmadinezhad is the right person for Iran. Well, almost. He really should tone down his war-hawk image, and his Israel-hating, but otherwise, he keeps Iran stable without turning it into a hellhole. There is some semblance of freedom in Iran, and at least it is not as strict as, for example, Saudi Arabia - whom we (as the US and the West) support.
Put Mousavi, and you will have chaos. For one,

the youth. Half of them, if not more, were just looking for an excuse to riot. This happens all the time. Nor does the youth have any understanding of real politics, or of what is possible in Iran, and what is not. Iran is a theocracy. You can slowly decrease the clerical influence, but this process is best executed slowly (unless for some reason you gain overwhelming popular support). My bet was that with Mousavi, little would change. If he tried to do any real reforms, that would be his end.
Too much instability. Iran is not ready for Mousavi. Try something centre-right - that by itself will be a miracle.
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