Whats wrong with preparing for nuclear war, especially if preparation is an effective deterrent to actual nuclear war. Ensuring a credible second strike ability

Whats wrong with preparing for nuclear war, especially if preparation is an effective deterrent to actual nuclear war. Ensuring a credible second strike ability is probably one of the more rational ethical actions someone can take outside of pacifism. Of course creating a credible second strike ability is so easy ( merely hide x weapons with delivery systems controlled by PALs ) that it has been a solved problem from the 1960s.