I don't consider it an assumption. Uber reduces transactions costs, increases competition, and improves the user experience of hailing a taxi. They are eliminating deadweight loss.

It is a quantifiable fact that the harm done to taxi drivers is outweighed by the jobs given to Uber drivers (quantifiable in the sense of dollars paid out - Uber has increased the size of the market).

> Uber is currently subsidizing ride costs with VC money. Uber can succeed in driving a lot of taxis/ride services out of business before the VC money shuts off and it implodes leaving people without ride services.

They are actually profitable in the US. However, this is true in many other markets, though I don't really see how its relevant.

> Airbnb can improve the efficiency by moving more people through unused housing. However, that can take away from long term rentals, and also brings problems with it like vermin (bedbugs, etc.) and transient crime.

Why is it a problem if it takes away from long term rentals? And i'm not sure how it would increase vermin, bedbugs, or transient crime, though i'd be curious why you think that might happen.

> Whose responsibility is it to clean these problems up? How do we clean those up? Or, do we regulate sufficiently up front that when damage is being done we have some limit to it?

If there are indeed negative, uncaptured externalities from these things, I think it's fair to price them in accordingly, through some sort of tax or similar system. But i'd like to see better evidence that these externalities are real.