I'm not OP, but from my point of view, the United States has been one of the most likely nations in the world to use its weaponry on others (by my count, it's currently involved in 7 military operations [1]), and has been involved in dozens more over the last few decades. It has formulated dubious reasons, and in some cases outright fabrications, in order to justify some of these military actions, and in doing so, has destroyed countless lives, a number of those innocent ones. That's not ethical.
The reality of the world is that yes, there are actors out there who will do others harm if they can, and one of the duties of a nation is to protect its citizens. I am not opposed to a true defense force, to protect against invasion. But once that military power is projected outwards in order to fulfill political and economic goals unrelated to national defense, then a line has been crossed and that behaviour can hardly be considered ethical any more.
I should note that I don't consider my nation, Australia, to be ethical on these matters either based on past behaviours (sometimes being involved in these very same conflicts).
[1] Afghanistan, Iraq, Syria, Somalia, Libya, Niger, Yemen