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.