I do think such laws have a very good and important role to play where people don't fully know what they've agreed to. If someone wants to get a job by offering their labor for less than his next competitor and is going into it with full information, I don't think we should act like we're doing him a favor by stopping him from doing so. Stopping someone from taking a less than minimum wage job has not alleviated their situation.
Again, just dispassionate observation -- mandating whatever number of sick days per year may be a humane gesture, but it doesn't change the underlying fact that there is a surplus of willing labor in this country willing to take jobs at these pay rates that even don't have any such benefits.
Efforts by unions to say that their political power and striking/etc led to change in our standard of living are conveniently mixed up with the rising general demand for labor and wages because we were a growing country willing to pay for relatively scarce labor at the time. Those conditions are not the same now.
If the employment conditions are transparent and not unsafe physically (which is related to having full information about what you're signing up for), why is sick days something that shouldn't be open to negotiation or a person willing to agree to have more or fewer of them?
Suppose that a person is young and healthy and believes he/she doesn't need a lot of sick days. Why is it unreasonable for him/her to agree to a job that doesn't offer extra sick days? What's the logic / principle there?
Is it because sickness is unpredictable and an employee shouldn't have to suffer from something unexpected? Is it an information asymmetry argument?