Down with Uber?

I seriously don’t understand the gripes against Uber and the like.
From the consumer point of view, obviously, it’s great. It provides a service that taxis and other livery services can’t–or won’t.
From the driver point of view, I don’t see the downside. 
Sure, they don’t get the benefits of a white-collar job, but many jobs don’t offer that.

What they do get, though, is an unprecedented level of autonomy:

• the ability to decide when, where, and for how long they work
• the ability to control their own work environment
• an efficient market that matches demand to supply (no ridiculous waiting at train stations for customers)
• a market that prices the service to demand 

It’s also possible to make a living wage with no boss. A top earner can gross $80k/year. If I’m not mistaken, gas and maintenance are deductible.
Even if you’re not a top earner, it’s not impossible to gross the national median of $50k.
Anecdotally, one driver told me she quit her full time job to do uber full time and made her previous paycheck in four days.
I’m not in a position to need a job as an uber driver. But, I used to be. I would have done it then in a heartbeat.
So… what’s the problem? How do ride-sharing services exploit drivers? I don’t understand.