> But it is not a Ponzi scheme. Last I checked, a local taxi company that is still in business wants $30 to take me into town, which is 5 miles away. Uber is $7.

The cost of that $7 are the billions they lose every quarter. It's not sustainable. They're a public company now, so to come up with fresh cash, they have to issue bonds and pay interest on them. How will they repay it when they aren't generating fresh cash through profits? They can't rely on VCs opening their wallets whenever they needed money.