There-in lies the rub.
Politicians are expert liars and manipulators. They have agendas. they arent always good, and almost always have some kind of barb in them. Positions of power attract those who hunger for power, and that hunger is insatiable.
What is "War for what I want" to the politician, he spins as "War to prevent $atrocity" to his citizenry.
As voltaire pointed out, those who believe absurdities, can be made to commit atrocities.
The absurdity is that there is a justification for war to begin with-- a "right reason." To the politician, that just means he needs to push that "right reason" button, and you will go to war for him, and he will get what he wants.
Be it "Spreading freedom" or "assisting a revolt" or whatever.
Think about what war actually *IS*.
"I disagree with you, so strongly, that I feel compelled to use lethal violence against you to either eliminate you, or force you to adopt my position in this argument."
When you look at war that way, all pretext of "right reasons" dissolves.
As I pointed out earlier, "War is necessary because war exists(elsewhere)!" is a tautology. That is what "Violence in the name of self-defense" is. "My violence is necessary because there is violence (elsewhere)!"