You gave two statements which are different from what I quoted.

The idea of "defend[ing] the United States and other democracies" and "defeat[ing] our autocratic adversaries" are always the stated reasons for US military action. Iraq was certainly an "autocratic adversary" and hundreds of thousands of people died from the war there. Vietnam was about "defending democracies" and resulted in millions of people dying. These are atrocities on an incomprehensible scale.

The ethical objection is very simple. War is evil, and the military is in the business of war.