To be fair, WW2 was essentially over BEFORE the US decided to drop the nuke on Japan. It was not "justified" at all and even if it was, if you have to "justify" something, you've likely made the wrong decision because you couldn't bother to come up with a better option.
Not to mention the fact that we dropped 2 bombs on Japan, 3 days apart (1st Aug 6th, 1945 / 2nd Aug 9th, 1945) AND 3 months after the end of the war with Germany, May 8th, 1945.
You're welcome to bring up their sneak attack on Pearl Harbor, but that was 4 years prior (December 7, 1941) to the US's decision to drop nukes on them, so that's pretty much irrelevant.
I'm not trying to say we should judge those that made the decision as fools for doing so, they did the best they could with the information they had available, but we can't keep looking at that situation and lying to ourselves that it was somehow justified when the war was over with.