Sure, but there are a lot of fields that aren't really that competitive (where you simply hire cheap laborers who basically work about the same), and where the pressure to conform may be higher than the pressure to find an employee that is 2% better than the next guy.
Even then, widespread aversion to hiring from one of two equally productive groups creates a big incentive to break the mold. And that incentive will only keep increasing as long as no one steps out. In the limit case, you pretty much have access to an 'unlimited' pool of free labor. This line of reasoning does presuppose a reasonably free country, though.
