Assuming zero other outside knowledge, this can be fine heuristic. But we do have ways of independently evaluating each risk on its merits.

Put another way, if you adopted this posture at the dawn of nuclear weapons you would be wrong to do so. Yes, you would be wrong to have done do even though we haven't had a nuclear exchange (yet). The risk is there. Arguing solely on the basis that it hasn't happened to date is like a gambler asserting he was 'right' when he bets the farm in Roulette and wins.

There are some caveats to the above but, unless you are prepared to assert no risk could be catastrophic, it is the correct posture.