They are shooting to become "too big to fail". Now the play with bankers, media and politics show that direction. There is surely no other way to change the law in their favor in the U.S., may not be so easy elsewhere.
For that the valuation seems right and may even have to rise. It's all on paper. Think of Uber as a global taxi and delivery-service - basically aiming to become a new monopoly or the strongest player there. Taxi is very fragmented with money going to lots of pockets. Uber is one pocket.
Valuations are about the best possible future. In that future , nobody uses a car but uses UBER to order a personal or a shared car(automated or manual). 17 Billion is nothing for that.
