The two main issues I have with them are that firms tend to give them to just about everybody (instead of just to folks working very directly with real IP), and they only pay base salary, not something closer to actual total compensation (often multiples of the base pay).
Having said that, the quant firm is relatively unimportant and not a good reason to prevent a total noncompete law. It's probably better to just ban them then try and make allowances that aren't full of loopholes.
While not impossible, non-competes without compensation are already hard to enforce as judges don't look kindly on preventing people from earning a living. The problem is the asymmetry of power let companies bully and intimidate ex-employees.
At least in some industries, however, there is a consumer protection/public policy argument against non-compete agreements, where: (1) there is no legitimate property interest to protect (e.g., the “trade secrets” held by the companies aren’t trade secrets at all because every company in the industry knows them), and (2) it is bad for consumers/against public policy to allow companies to use non-compete agreements to stifle competition where there is no legitimate property interest to protect.