Without someone vetting these drivers and taking a risk and responsibility for people's safety, this seems like a terribly dangerous way for anyone to get around.
I don't see why LibreTaxi, in areas that have a individual driver licensing scheme, couldn't require that. You just look at the driver's license when you get in, or they post it on the back seat. The license information is recorded in LibreTaxi so everyone knows there's a paper trail if anything happens.
This would be identical in safety for everyone to medallion hailable cabs, or am I missing something?
If I was going to do nefarious things, I wouldn't bother with any of that. I'd instead just carjack a taxi and have at it.
Or hopefully they would rather not, at least if they are serious about it and are not just running on a short-lived inspiration to play pretend-Kalanick.
Criminals aren't liable to want to leave an electronic trail driving a taxi just to rob someone. It's likely to be nearly as safe as riding Uber or Taxis in general, which is to say extremely safe.
What's more likely is the driver will get robbed, but even then that's not going to happen very often.