I didn't say I'd fight against the existence of the law. I said people who are hurt by the law should retain the same negotiating power they had before rather than lose their right.

You won't lose any negotiating power. Just because they can't ask doesn't mean you can't counter an offer and ask for a higher salary. If they want you and think you're worth it, you'll get it. Just don't see them not being able to ask really shifting the negotiating power much if any for you.

Likewise, just because an employer offers a lower salary than you want based on your salary history doesn't mean you can't counter with the salary you want. If they want you and think you're worth it, you'll get it.

The benefit of telling a prospective employer that a previous employer decided you were worth an above-average salary vs. simply requesting an above-average salary without context is obvious.