Your point has wandered a bit
And I apologize for my part in it.
Now we seem to be talking not about people being Marxists (whatever tiny but terrifying percent of the population that they make up), but instead about teachers using class time to preach Marxism. Who could be for that? I'm against any teacher using class time to preach about anything. In my experience, though, it was harder to keep teachers from going on about their personal lives than it was to keep them from preaching anything.
I don't recall ever hearing about a case where a teacher was caught preaching Marxism in an American classroom. Are there really cases of this?