It's simple: In this specific case, the thug in question hates GW Bush, they hate GW Bush, so they (from the leftscum point of view) are on the same side. More generally, you will find very little criticism of Islamic and left-wing dictators on the left.
Check out this diary and comments on Daily Kos: http://www.dailykos.com/storyonly/2007/9/24/143116/861 A couple of the commenters mention the whole "there are no gays in Iran" thing. Most are studiously ignoring it. This is classic cognitive dissonance: In their worldview, GW Bush, Christians, and conservatives are the only real evil. Anyone who opposes GW, Christians, and conservatives is good. Good people would not say such a thing. Therefore, the fact that Imadinnerjacket said exactly that simply is not registering in their "minds."
Scary, eh?
Isn’t it an old Arab proverb that ‘the enemy of my enemy is my friend?’ Since the ULTIMATE enemy is Bush, Ahmadinejad and the American Left are supercozy. All other differences are irrelevant.