My uncle, a protestor, still hates my father, a veteran, for going to Vietnam.
So, yes, the animosity towards those in uniform existed. Was it as bad as portrayed in the popular media of the 80s? No, it was not. However, it was bad enough to make veteran status a protected class for job discrimination.
As for the POWs, there was just enough rumor and sightings to keep the interest going. I was peripheral to some of the groups involved in that activity. I met with the author of this book in his office in DC:
So, take the perspective of the Vietnam veteran feeling less than welcome. Add in some good rumors of sightings. Add in some random statistics that makes things sound worse (e.g. pilots tended to be found, but back seaters were not - perhaps because their knowledge was worth more?)/
All of that is enough to create a nice cottage industry of both well meaning people who want to bring the boys home, and professional searchers for random bits of data just simply making money off of misery.
Final part of my ramble - my grandfather was an intel officer. Among other things, he debriefed POWs from our Korean debacle - including 2 who escaped AFTER the war was over and all POWs had supposedly been returned. So if you ask me whether or not I believe that it was possible that all POWs were not returned? Absolutely possible.
Are any left now? I sincerely doubt it.