They can't guarantee flexibility and full-time employment. That's the point.
>"Americans shalt work from nine until five so sayeth we the founders".
If there is no demand or there is over-supply at some particular time in some particular area, you can't will a job into existence.
>They're just griping that they need to start paying benefits.
Are they griping? The costs are going to be passed down to the consumer. They will still be more competitive than taxis (which are still abysmal with customer service). And by raising regulatory costs and requirements, you're making it harder for any new entrants to come in and compete. Sounds like Uber and Left break-even, and everyone else loses. Alternatively, if this new regulation kills Uber and Lyft, then everyone loses.