Moral Equivalence

Now the excrement is really hitting the blade driven nitrogen/oxygen agitation device.

Let's take a step back. There's been a lot of talk in the UK since July 7th about moral equivalence. I've been thinking about that today. Here's a half baked thought on the subject.

It is not possible to justify the actions of the terrorists who killed 52 people on that day in London. The deliberate targetting of civilians in this way is absolutely unacceptable whatever their motivations. The "root causes" of these actions are irrelevant. The fact that they believed that they had a just cause is also irrelevant. Even if they genuinely did have a just cause, the actions themselves can never be justified.
Why do we say that?
It's because they deliberately killed 52 innocent people. This is simply unacceptable. End of argument. I agree with this in it's entirety. It's rock solid.

What happens if we extend that argument to include the actions of nation states though?
An example.
In 1945, the US government ordered the bombing of Hiroshima and Nagasaki. According to Wikipedia, these actions killed 120,000 people immediately and around 240,000 in the aftermath. They were primarily civilians.

The deliberate targetting of civilians in this way is absolutely unacceptable, whatever their motivations. The "root causes" of these actions are irrelevant. The fact that they believed that they had a just cause is also irrelevant. Even if they genuinely did have a just cause, the actions themselves can never be justified.
Why do we say that?
It's because they deliberately killed 300,000 (my estimate) innocent people. This is simply unacceptable. End of argument. I agree with this in it's entirety. It's rock solid.

What's wrong with this argument then? I genuinely can't see a flaw as I write this. I accept that there might be one but what is it?
It seems to me that nation state violence is acceptable just because it is. Or rather, just because we say it is. So is it really the action itself we find so appalling, or are we only appalled when these actions are aimed at us?
Just a thought.