Last Friday it was reported that Uber, the transport technology company that links passengers to drivers with its smartphone app, had raised $1.2 billion in a funding round valuing it at $18.2 billion.

The valuation means that Uber is worth roughly the same as Hertz Global Holdings Inc. and Avis Budget Group Inc. combined. As The Wall Street Journalnoted, “Only Facebook Inc. in 2011 raised capital at a higher valuation from private investors — an investment from Goldman Sachs valued the social network at $50 billion—according to VentureSource data.”

The reaction to the news has been mixed. In The Guardian, James Bell, who described the valuation as a “fantasy,” wrote the following in the wake of the news of Uber’s valuation:

… when you buy a tech stock at a huge multiple – and Uber’s revenues have been (generously) estimated at around $200m a year, which makes $18bn a borderline-insane 90x valuation – you’re making a bet that its profits down the line will be vastly larger than they are today. In fact, you’re betting that they will be almost unimaginably larger.

There is absolutely no reason to believe this is true. Uber has rivals in every market it’s in – both established players fighting off the insurgents, and Uber-like rivals with similar software products. Uber and all its rivals are dueling one another for taxis – lowering fares and their percentage takes, even offering lunch or $500 bonuses to drivers.

The Wall Street Journal’s Christopher Mims has described the valuation as “nuts,” and wrote that the “moat” protecting Uber from competition is “incredibly shallow,” arguing that drivers are driven by price rather than loyalty to Uber. Mims went on to say that the market Uber works in will remain easy to enter despite any of its attempts to deal with competition:

I say ride-sharing is “frictionless” because in its price war with Lyft, both companies are forced to constantly lower prices, and riders — especially those whom the company presumes will give up their cars — are naturally price sensitive. Even if Uber uses its funds to try to crush competition such as Lyft, the Lyft model is simpler than Uber’s and built on recruiting everyday folks, not professional drivers. It isn’t hard to enter this market.

Mims also argued that even if Uber captures 50 percent of the global taxi market in five years it would still be worth less than $18.2 billion.

However, over at Vox, Matthew Yglesias correctly points out that Uber and its competitors could greatly increase the size of the market for paid rides, which seems to be what Uber CEO Travis Kalanick has in mind. In a recent interview with The Wall Street Journal Kalanick said that Uber’s vision is, “Basically make car ownership a thing of the past.”

In Forbes, Mark Rogowsky writes that Mims is wrong to treat Uber as a replacement for taxis:

So long as you look at Uber as a taxi replacement, you’ll see it as something less than it’s already becoming in its early markets: A transportation app. In San Francisco, for years the taxi commission didn’t want to issue more medallions for additional cabs because there was ostensibly no real demand for them (As of last year, the city had 1,600 taxi medallions). Yet just 4 years after Uber’s launch, there are often well over 1,000 rideshare vehicles on the road during peak times.

Rogowsky’s article highlights two important points to consider when thinking about Uber and its competitors: 1) Unsurprisingly, bodies like San Francisco’s taxi commission are evidently not very good at estimating the demand for rides, and 2) while Uber is competing with traditional taxis it would be a mistake to think of it as a taxi replacement rather than a technology company that makes it easier for passengers to find drivers, be they professional chauffeurs or car owners trying to make some extra money on the side.

What makes the huge valuation especially remarkable is that Uber and its competitors are facing numerous regulatory challenges, some of which I wrote about last week. Yet despite these challenges, investors see an opportunity in Uber. Speaking to Reuters a spokeswoman for Summit Partners, one of the investors in the funding round, said, “Uber is one of the most rapidly growing companies ever, and we believe there are opportunities for continued tremendous growth.”