War is bad. Defending against war, that can be justified. But
starting a war, well that is presumably very bad. Not that starting a
war could never be justified. Just that the bar should be set really
high. Not it sort of seems like war might help something. No you, and
those watching you, should really worry that you are accepting excuses
to start a war for other reasons.
Among all the policy arguments I accept, the above argument against war seems among the most solid.
The main sticking points: I'd have to convince him of two things: