Can't really comment on that as in my city (not US) to drive for these companies you need a license. To get the license, they perform background checks, check your criminal record, ask for medical approval, etc, every time you have to renew it, and all this seems to stop a lot of bad stuff. Not saying it doesn't happen - you can't never completely stop it - but there are ways to reduce it.

Anyway, they could just allow customers to select their preferred gender, would make anyone that wants to use such option happy, and we wouldn't even have to talk about discrimination.