The software and hardware has been extensively tested on test tracks, they built a whole fake road system in Pittsburgh[1].

Even drug companies can't know what they don't know and end up killing people with extensively tested drugs. Airplanes fall out of the sky because of unknown bugs that simply cannot be reasonably tested for.

Human progress relies on taking mitigated risks.

[1] http://www.businessinsider.com/ubers-fake-city-pittsburgh-se...

Random untested people without driver's licenses and people who no longer possess the faculties to drive safely are on the road all the time. You're being hyperbolic.