Regardless of whether it was an accepted idea, a great many nuclear devices have been tested without causing nuclear winter. Presumably you’d need a nuclear event even more energetic than Krakatoa (and probably much more energetic because Krakatoa provided its own dust) to get equivalent effects. Krakatoa didn’t exactly wipe out the human race.
We could argue all day about how plausible or implausible a large-scale nuclear strike (as opposed to smaller tactical strikes) would be in the absence of a MAD policy and not get anywhere.
