Again, this is a conceit both von Ahn is more than willing to make, because there is a higher ethico-moral purpose being served. The irony is just almost unbearable - Von Ahn: “We could do other things, like digitizing checks, but banks already make enough money.”
reCAPTCHA takes something that the user was already forced to do by capitalism and puts them to work for capitalism. We acknowledge that obviously UBE and spam is an annoyance, and potentially dangerous if filled with malware. But so is advertising and marketing in general. It is just that those industries have finally gotten so good at doing it the distinction between art and the market, between ads and entertainment, between work and play, has been eradicated. Ads can be fun, too. Forget football, we watch the Super Bowl for the commercials.
The problem with UBE is that it was never allowed any legitimacy or space, always defined as criminal, because it was a problem for business. The limited legislation on the books for UBE does not even address its most common form. So, again, capitalism must solve its own problem with its own tools, allowing room to perfect those tools in their form, design, and function. Easily and deliberately lost in translation (as code is most certainly far from the vernacular) is that the ultimate function of capitalism is the generation and regeneration of more capital, achieved in part through the perfection of exploitation. Pleasure in the job, perfection in the work.