Having grown up in the 60s and 70s, I'd say people took nuclear war seriously. People had different opinions on how likely it was and whether it was an extinction event, but there was near unanimity that it was "a really bad idea." The obvious difference was that was impossible to doubt it was man-made and it wasn't something that slowly built up over decades--there was no way to say it was "normal"
I think it’s a fair point to say it was considered as a serious threat to certain countries(US/Russia/UK/China etc). And militaries certainly did prepare for it. But other than Switzerland with all their bunkers - which society in all facets prepared for it, really?
WW2 with it’s restrictions & rationing, and almost all civilian economy/effort being redirected to the military is I think what a lot of people are wanting in my honest opinion.
