We must begin by acknowledging a hard truth. We will not eradicate violent conflict in our lifetimes. There will be times when nations, acting individually or in concert, will find the use of force not only necessary but morally justified.
And tell him it's quite true that the best of the philosophers are of no use to their fellows; but that he should blame, not the philosophers, but those who fail to make use of them.
If a person who lives in God becomes miserable, what is the use of living in God? What is the use of such a God? Throw such a God overboard into the Pacific Ocean. We do not want such a God!