Earlier quoted context omitted.
Hippies were until they weren't. Counterculture either becomes culture or dies off. Naziism was counterculture in 1920's Germany, Mainstream in the 30s and 40's, and back to counterculture now.
An argument could be made that there is a lot of ideological overlap between current far right GOP/Qanon people and the tenants of Nazism. Considering the number of elections won by the GOP you cannot tell me they're not mainstream.
It just means that some parts of their platform have become mainstreamed. A simple and non-controversial example is that the Nazis were extremely Progressive on animal rights. Just because modern political parties also endorse animal rights, that does not make them Nazis
Another example is that Nazi rhetoric relied heavily on utilitarian analysis of the greater good. I don't think it's reasonable to say that any party that promotes the greater good over individual freedoms is a Nazi party.