An interesting point, but I don't think that's actually true. I doubt there are many places where you'd actually get in trouble for reading the Communist manifesto.
(But admittedly, this is spoken as someone who mostly has exposure to more liberal workplaces - so I'd be happy to be corrected if I'm wrong.)
What has always confused me about this discussion about say, a left leaning bent at Facebook or whatever is that this has always been the norm in virtually every conservative place, which is like 90% of provincial small towns, from which all the liberal and creative people have to run away in the first place.