I think the main difference here is that the nazi's were actually doing bad things as well as saying bad things.

In this case, bar the rare exception by individuals, these are people who are vocal that they think they're superior based on a superficial biological trait and nothing more.

If you think the current crop of neo-nazis has the same clout and power as the WW2 ones, I have several bridges to sell you.

The USA didn't go to war against the Nazis until they had gone well beyond even the most terrible actions, let alone speech. Almost all of Europe had already been conquered, the last holdout in the UK was getting pounded daily and the US still didn't join until attacked directly.

The core difference between then and now is that America of the mid 20th century didn't believe ideas were inherently dangerous - even the communist threat led to at worst the McCarthy hearings which are universally regarded now as a stain on America's history. What we see today is lots of Valley Ivy League graduate types who are convinced that reading a few tweets of the wrong kind wipes people's brains and literally turns them into the third Reich, in ways that nobody can stop or control. But there's no evidence for this viewpoint, and arguably it just led to the largest and craziest conspiracy theory in American history (the idea that Trump is a Russian spy).