Great comparison with pre-Code and post-Code movies, and agreed.

We would not have Vietnam-set movies with any nuance otherwise, and they absolutely and acclaimedly exist.

Absolutely, and they weren't all made in the 70s, either, but went on being made during the Reagan era. However, presumably it helped that the general cultural climate in the 1970s encouraged said nuance, and that of course most of the film makers were of that generation, with protests etc. a very recent memory lingering into the present.

Incidentally: it's a cliché that I've seen repeated not just by Republicans but by many Democrats that what ultimately cost Carter the election was that he talked about America's malaise whereas Reagan told the US about its greatness etc. Which, okay, but now you have the Orange Menace who swept into power by telling America how rotten everything. Presumably the difference is that Carter didn't blame outside forces and/or his political opponents?