He really was amazingly hawkish. Even secular anti-Communists were impressed by his commitment to extending American military power.
But his wiki article says he opposed the Vietnam War. So in practice he was actually quite preferable to most of those and nowhere near as destructive.
Well, yes, and he admitted that the atomic bombings of Hiroshima and Nagasaki were wrong. I reiterate that for a Christian theologian these are
very low standards, and it's as a
theoretician of religion as a justification for the extension of political power, rather than in his specific good or bad positions, that Niebuhr's awfulness really shines. Even then, you're right that there were obviously far worse and more damaging people in American religious life at the time--Francis Spellman, for instance, or Oral Roberts.