Would it be correct to say that mistreatment of Vietnam veterans was isolated and not widespread, but that it did happen? It would seem that way, from what I have learned. My grandmother said she saw mistreatment of Vietnam veterans on the News. Her brother (my uncle) was a Vietnam veteran who earned the Purple Heart in Vietnam. I never asked him if he was mistreated by the public, and neither did anyone else in my family. Even if we did, he would probably not have wanted to talk about it (nor did he want to talk about fighting in the war).
There is always more to be said, but you may be interested in our Vietnam War FAQ section in general, and this previous answer by /u/Bernardito:
Why were returning Vietnam soldiers treated so poorly by the US public?
He also addressed this matter in more recent follow-ups in Did soldiers really get spit on coming back from Vietnam?