It's definitely a moral conundrum as evidenced by the U.S. civil war, the two World Wars, and some interventions in genocides, contrasted with the lack of intervention in other genocides or in Soviet and Chinese (to pick on the largest) mass murder/starvation of citizens for political reasons.

I agree that equally powerful societies face the hardest choice; whether to risk everything to save everyone or to knowingly allow atrocities to continue while preserving themselves.