If you happen to have watched last night's episode of "24 hours in police custody," you'll have seen a perfect example of why someone being a vetted and licensed taxi, or private hire, driver doesn't protect people to any greater degree. At the end of the program, the creep in question (a taxi driver who had raped a 15 year-old child, and a young woman) got a 22 year custodial sentence.
I think that maybe Uber's vetting process is no better or worse than that of licensed drivers. After all, the best it will ever manage is filtering drivers who have not (yet) been convicted of anything. The real root of the problem is twofold; passengers implicitly trust the stranger driving them around because of deference to authority, and we live in a culture where peope turn a blind eye to rape, sexual assualt, and other forms of violence. You can't do much about the former, but you can improve the situation of the latter with education.