To be clear, I do agree with everything you've said here — I just disagree that freedom of speech is an inalienable right, and I don't think there's ever been a time or place where it has actually been considered one.

If it were up to me, I would require non-disparagement agreements to be standalone contracts, and cap the damages a company can claim to the amount they paid you to sign it. Once that number is met, the contract is void. That way the company only gets as much leverage as they're willing to pay for.