Peter Beinart and the benefits of Twitter

Norm brings up a question asked by Peter Beinart on Twitter:

? for war supporters: why is Iran/Hitler analogy better than analogy w/ Stalin getting nuke in 1949 or Mao getting it in 1964?

Norm's own response to that:

One could turn that around. Why isn't it a better analogy?

I am not sure whether Mr Beinart is genuinely baffled by the question he twits tweets around or, possibly, there is some deeper meaning to it. In any case, I would like to turn it around another time.

Why indeed, dear Peter? And how, precisely, it matters?