I think it was US who was most likely to launch a nuclear atack with the religious right in full power in 1983. Although I imagine Reagan wasn't quite as "close" to God as Bush was.
Whereas Marxism, believes in historical determinism, it is materialistic in essence, so if all human life gets wiped out, there would be no chance for communism to develop. While Christian Right is metaphysical in nature. And, you know, "immortal soul" cannot be touched by radiation fallout. And even if every last human "leaves out this world", there is there a better world for believers.
For that reason, there is a scene where the mother is angry with God. I believe she is angry with people who took the risks of destroying this world (in the hopes of eradicating the "evil empire"), knowing there is a better one out there.
We are lucky that Gorbachev was such a pushover. Had it been somebody as cavalier in the power of USSR as Reagan was, we would totally see a nuclear cataclysm, with US striking first.