I think Uber should do background checks. I think the chances of sexual assault are considerably higher walking down the street than getting a cab/Uber the same distance.
I'm not so sure, we'd need to look at statistics for that.
Regardless background checks should be done; just like cleaning checks in commercial kitchens, you may be more likely to get sick from home cooking, that seems largely irrelevant.
Another analogue: Most child sexual abuse is by family members, I don't see that as a reason not to do background checks on care workers.
Do you really consider it acceptable for Uber not to do legally required background checks (DBD, health)?