It's an attempt to make an abstraction concrete. Think of it as the trolley problem in real life.
Stalin is famously supposed to have said, "one death is a tragedy, 100,000 is a statistic". Cynical or not it is how humans think.
> If you believe we should never use nuclear weapons, then don't have them at all.
Strategic game theory and Mutual Assured Destruction depend on the possibility that the other guy will use them if you do, and may be the only way to prevent their use. Interestingly this is one reason why you want the other guy to know your procedures, capabilities, deployments etc. Secret weapons have no deterrent value.