"We haven't died yet" is the most selection biased evidence you could possibly invent. 10 on a scale of 10.
It also has no predictive value given the nature of catastrophic threats continues to evolve rapidly in quantity and quality, and the elements of past threats (the cold war -> nuclear war), continue to be threats (autocratic regimes -> fighting or planning wars that could become existential to their leaders -> nuclear war).
Given we have a sample size of one, its hard to make argument not based on past experience as that's all we have to go on, and we a reasoning about use of weapons that haven't existed for a century yet it hard to make strong argument either way bit MAD seems to have worked so far and most leaders of nuclear armed States are to egotistical to commit suicide when they are living the good-life at the top and that's what launching WMD s, is its is suicide .
It also has no predictive value given the nature of catastrophic threats continues to evolve rapidly in quantity and quality, and the elements of past threats (the cold war -> nuclear war), continue to be threats (autocratic regimes -> fighting or planning wars that could become existential to their leaders -> nuclear war).