Having said that, I think the airbnb market in NYC is reasonably close to clearing with the hotel market. Probably some listings for very nice apartments and also some for relatively mediocre apartments are underpriced, but the truth is that a night in a decent airbnb apartment is in general commensurate with the cost of a hotel room in the same neighborhood.
The catch, of course, is that there are many airbnb listings in places without hotel rooms at all - Harlem, the far Upper East Side, etc - and in those areas the airbnb prices appear low but of course we don't know the appropriate hotel room clearing price.
But to your basic point, I agree there's probably some discount right now for the general sense that airbnb is "weird" or "idiosyncratic" to the average traveller.
> the cost of adjusting for the externalities will erase the savings of AirBnB
is false, which is more or less exactly what I’m trying to get at too: it is not unreasonable to expect that AirBnB will continue to be cheaper than hotels even if externalities are priced in.
As for hosts being less dependable, I’m sure that happens, but the few times I’ve used AirBnB, I’ve been quite pleased. By contrast, it seems like more than half the time I check into a hotel, something is amiss or the room isn’t ready by the time it was promised, or ... something. There are exceptional hotels with great customer service, but most hotels are borderline terrible in my experience.
I'm not saying there aren't great deals out there on AirBnB; right now it's a market of people basically selling unused inventory at very low prices. I'm saying that if they had to incur more normal requirements (safety, taxes, insurance), the pricing would rise and the inventory would decline. If that same AirBnB room cost $250, it might not as interesting to you.