But, Squink, the question raised by the OP is not whether the US (or any other state) is morally obliged to defend the human rights of the citizens of another state, but whether it is entitled to do so.
I grant you, if you conclude that the US has a right to do this, then then question of whether it has an obligation to do so arises. But not until you conclude that.
The OP mentioned Nazi Germany. Is it your contention that, because the Jews of Nazi Germany failed to “rise to their own feet and throw off their shackles”, other states could have neither the right nor the obligation to come to their assistance? Cases in which a government terrorises an entire population are egregious; cases in which a minority is abused with the support, or the assent, or at least the indifference, of the majority population are much more common.