I assume the idea behind refusing to work with recruiters who have been unethical in the past is to create a disincentive, in the hopes of reforming the economics of recruiting so you can get recruiters who will work with you rather than against you.

You'd imagine there would be some recruiters who would aim to behave ethically and to cultivate a reputation for being ethical, as that reputation would be valuable to a recruiter in terms of getting clients.

The one time I was job-hunting I saw some pretty unethical stuff - I once had a recruiter e-mail me a programming test along with a solution another candidate had submitted, and almost every recruiter asked for a summary of technical interview questions so they could brief other candidates. I would have thought using unethical recruiters would actively hinder your recruitment process - so there'd be no market for their services.

I mean, evidently it doesn't work that way, but I think that's the aim of refusing to work with certain recruiters.