So you believe there should be taxi services which can skip the background check but otherwise can have their cars look like any other taxi service?

Uber may do the checks voluntarily, but having no regulation means you wish for a company that can refuse to do so.

I think generic laws/jurisprudence that, in a court, would find those companies guilty of negligence (and heavily punish them) if they hadn't performed standard checks before hiring[1], would be more than enough to convince every company to check.

[1] http://en.wikipedia.org/wiki/Negligence_in_employment