I don't agree. Selling a gun to a hunter is not the same as selling a gun to a known child murderer. Both is "just" selling a gun but they are very different in practice.
Usually people making your argument also say that private corporations can and should moderate speech. Do you support that? If so, then why do you disagree with workplaces banning topics?
Corporations setting workplace rules have no impact on your freedoms. You're free to work there or quit, or suffer the consequences of breaking their rules.
How do you decide this? Your intuition? The clothes someone is using? The way his talk?