Completely depends on the situation. Something like nuclear weapons are not a black and white issue that can be instantly written off as right or wrong. In a specific instance, such as the bombing of Hiroshima and Nagasaki.....they're something horrible and appalling, but yes, absolutely justified. The cost in lives to both the Allied forces and the Japanese themselves if Operation Overlord (the fullscale invasion of the Japanese home islands) had been done would be astronomical and absolutely unacceptable.