I’m pretty sure the concept of a white knight predates the KKK and that’s something they appropriated from earlier medieval culture.
I imagine amongst pimps you’ll find many who are abusive the way you imply (taking way too many of the proceeds). At the same time, there might be some who are just glorified bodyguards who are there to protect a sex worker from abusive clients and make sure clients pay.
IE stuff you wouldn’t need if sex work were legalized because then police could do more to serve in that role for independent contractors.
The idea of “completely free choice” is an illusion, since probably the majority of people work in jobs which they’re prefer to give up for leisure or an easier job if they could find that alternative. The need for money is a coercive force in all occupational choices.
I acknowledge that there are people pressured to work by someone abusive, and who have histories with addiction. You’ll find this in many occupations beyond sex work though, like working in fast food.
I don’t think exploitive pimps would actually want sex work legalized because then they wouldn’t be able to use the illegality to monopolize the protection racket.