I think the part of the sentence missing in your quote ("while reducing housing availability which primarily impacts lower classes") explains his stance.
Usually businesses catering to the upper classes don't usually do so at the detriment of "the poor". For example Ferrari selling 100k+ cars doesn't prevent me from buying a cheap car. Homeowners renting to "rich people" prevents a poor person from renting the same apartment.
This could of course happen with regular rentals, but the difference is that nobody would pay above market rates for a long-term rental, which is what basically happens with Airbnb.
I mean "above the rates of the long-term rental market".
I think the argument is that Airbnb and similar take those apartments from the long-term rental market and put them on the (very) short-term rental market, aka the hotels'.
The problem put forward by those arguing against Airbnb is that this is a zero-sum game. If you have tourists who are able and willing to pay more for a flat (aka "middle or higher class"), this reduces housing availability for "the lower classes".
You could, of course, argue that this would be true even without Airbnb if enough "higher class" people wanted to live in a given city all of a sudden. I suppose that's why people also tend to be against gentrification.
> this reduces housing availability for "the lower classes".
Only in the areas that are popular tourist destinations. I guess that's something that NIMBYs seem to care about that I don't identify with at all. Why does it matter if poor people can afford to live in the hottest tourist areas? As we can very clearly tell from the price signals, being there doesn't benefit them nearly as much as it benefits the tourists.
As you say, the same thing applies to the long-term housing market. The price signals are telling us that there's a large social benefit to having higher-productivity workers living in urban zones, and there's an opportunity cost associated with displacing (counterfactual) high-productivity workers with low-productivity workers.
If I build a factory that dumps toxic sludge into the water supply, that’s not sustainable and yet it might be quite profitable in the absence of regulation.
Airbnb doesn't have massive uninternalized externalities. The preconditions of the Coase theorem are pretty close to being met when it comes to house rental.
> It is extremely classist. Only something that middle class or higher can use
So you think any business which isn't affordable to everyone should be shut down?