Should we apologize for Hiroshima? If we do, perhaps then we shoul;d apologize for invading Berlin?
The fact that we saved millions (land invasion) by killing hundreds of thousands is a utilitarian argument I will not take up.
Will Hiroshimas occur again on Earth? Its just a matter of time, not if. Just as more Pearl Harbors will occur, and more Prisoners of War will be starved and tortured, and more enemy soldiers will bayonet babies, at some point, in the future.
The US should not apologize, but demand an apology from Japan. Period. There is such a thing as right, and a thing called wrong. And force is morally right when it is in response to the initiation of force.
I only bow to fallen US soldiers.