> because lawmakers think workers are metaphorical babies.

To be fair, there's a long history of abusive employers, so it's wise to try to tilt the law in favour of the employee as otherwise they get exploited even more than usual. The nature of employment is typically skewed as employers will have a lot more power than the employees - that's why Unions were invented to try to redress that balance.

> You can have a look at contracts between equals to see that being able to restrict yourself is important.

There's an important distinction between restricting yourself and signing away inalienable rights. You can certainly agree to restrict your speech so as to not embarrass your employer or give away secrets, but signing away your right to liberty is different.