let's say you think capitalism is evil, destroys the environment and the essence of humanity, etc., and you say that in public. wouldn't that also call into question your ability to be an effective employee and work towards the interests of the company? wouldn't we all be very upset if someone got fired over that?

I don't really disagree with your specific example (or that there have always been things that you can't really say in america), but in general it's a shitty way for the world to work. we should seek to change it.