This is just another example of how employment laws in the US are skewed incredibly towards the employer - add to that the deceptively named "right to work" laws. Having come from a country that for 100 years or more has a much greater tradition for protecting the rights and conditions of workers, I am sometimes appalled at what I see here. (remember, not all the right wing propaganda condemming trade unions is true)
in reply to Professional Employees and Works for Hire
One method that would be well worth looking into is to work as in independant contractor - set up your own company, and have that company employ you. Your company then contracts you to the client, and there are quite specific terms and conditions on IP, copyright and the rest.
The other approach is, at offer of employment time, ask for and review a copy of the company's IP agreement, employment contract and so on - all the things that you are being told to sign - and strike out those clauses that infringe on your non-working hours activities.