The key part is "...has a dangerous probability of creating a monopoly for the discounting firm".

That's not the case here. I don't see Uber creating a monopoly in any way. If they raise prices to unreasonable levels (i.e., more than people used to pay for regular cabs), people will go to Lyft, Juno, or the next ride-hailing startup. If there's no competitor remaining, new ones will show up. Or regular cabs will be back.

IMO, the endgame for Uber is not to raise prices; it is to reduce costs. They're betting the farm on driverless cars.

Not too different than Amazon with retail. Amazon doesn't need to charge more than the local retailers they've put out of business; they just need to have a lower cost structure.