> I highly highly doubt they pumped 21.7 BILLION FUCKING DOLLARS
There's the legend about the Texas oilman who, wanting to distract his competitors, started a rumor that oil'd been found in hell. This worked for a bit, but eventually he heard the rumor enough times himself that he had to go check out hell for himself.
I personally wouldn't be shocked to find out Uber never ends up really working as a business. Investors are herd animals, and hate missing out on a hot deal. By your logic, nobody would have given Theranos $1.4 billion fucking dollars without making sure their shit worked. But we now know it was a fraud, and not even a very good one.
It's very hard to know if the unit economics for Uber work because there are a lot of things muddying the picture. Uber doesn't own the cars or employ the drivers, so capital costs and expenses are mostly on other people's books. Uber is getting a massive subsidy from investors, but it could also be argued that it's getting a massive subsidy from desperate and/or optimistic drivers who aren't properly valuing their cars, their time, their sanity, or their health. Uber is definitely getting a subsidy from society: they're creating large externalities in terms of pollution, congestion, and carbon emissions. And probably also in terms of short- and long-term draws on the social safety net. Over time, things tend to be properly priced, so Uber's unit economics will likely get worse. We just don't know how much worse.
And even if the unit economics end up being positive, Uber has a lot of investors who expect a return. Given that they have a very shallow moat, will they be able to throw off enough profit to satisfy shareholders without competitors coming in and undercutting them? If they're going to give the same kind of return on capital as Apple, I'd guess that will take $1-2/ride on its own. That could be quite an advantage for a scrappy competitor.