Let's say in your heart of hearts that you earnestly thought that, for whatever reason, women couldn't be effective software engineers. If you said that in public, you should be fired because it would immediately call into question your ability to work within your team, your ability to respect your co-workers, and potentially bring negatively adverse financial consequences to your place of work and damage its reputation.
Now, I don't know what you actually believe, but it's worth noting that you currently have all the free speech you want and have always had. What you're arguing for is free speech AND no consequences, which isn't and was never guaranteed.
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.
Now, I don't know what you actually believe, but it's worth noting that you currently have all the free speech you want and have always had. What you're arguing for is free speech AND no consequences, which isn't and was never guaranteed.