> They don't need to provide a reason

Of course, since they did not ask for the congress approval, which is already against their own constitution. That's exactly the kind of things you do when you're a good guy doing the right thing

> but the norms of not attacking third parties etc are there for rational reasons, since you don't gain anything for doing so its just stupid and causes damage and strife and hurts you for doing it.

What norms? No wars = no rules of war, they started something they can't control anymore

They gain plenty from doing it in term of leverage, nobody attacked Iran in such way until now because it was well understood that this is exactly how it would play out