"The fact that this is not a legitimate argument can be evinced by the simple fact that this horrible act has never been repeated in history."

This is not an argument, it's not even rational.

The first reason that 'that decision has not been made again' is because international actors since then have to take into consideration that outcome.

If that situation were duplicated, the bomb would be dropped again.

Eisenhower ordered a demonstration of tactical nuclear weapons which decisively 'ended' direct hostilities on the Korean Peninsula.

Were the Chinese to have continued their advance, then 'nukes would have been used again'.