The U.S. is in no position, morally, to think we have the right to defend other nations that we feel are under threat.
As a part of NATO, yes. Otherwise, your thesis defends the American invasion of Vietnam. The justification being that Vietnam was going to fall under the spell of some sort of monolithic communist takeover of the world.
Ditto for Chile and the removal of Allende. How about them Dulles boys and Guatemala? Who are we protecting, again?