False dichotomy. There are other ways to deal with Iran that don't involve starting an ill conceived (and illegal) war that kills school children and possibly (probably?) plunges the world economy into recession. It is highly unlikely that the current military action will result in a pacified Iran.

Why do people think that since Iran is evil all actions against Iran are justified?

They're not old enough to remember the start of the war in Iraq, I imagine. For those who aren't: it was a barrage of justifications which were found to be untrue, especially the 45 minute claim which said Iraq could strike European targets within 45 minutes with chemical or biological weapons. The UN weapons inspector said this was nonsense, and so it proved to be - after the invasion.

Iran will go the same way, one way or another.