I'd say AirBnb increases travel by decreasing the cost of housing. It increases supply of an otherwise dormant asset. I agree that to argue that it has no effect on privacy of neighborhoods or crime is naïve. On the other hand, lowering the cost of international travel[0] enables more people to travel and to be exposed to more of the world. This is, in my view, a positive.
[0] San Francisco<->Milan Oct. 7-21: $522 on Lufthansa
> I'd say AirBnb increases travel by decreasing the cost of housing.
It decreases the cost of housing for tourists by decreasing the supply of housing, and thus increasing its cost, for locals.
> This is, in my view, a positive.
There's many ways where increased travel can be considered a negative such the increase in greenhouse gas emissions. I'd also consider if that positive truly outweighs the negatives on the locals of an area. Hotels work just fine, and are accounted for in city planning.
[0] San Francisco<->Milan Oct. 7-21: $522 on Lufthansa
$22/night, 4.93/5 Rating: https://www.airbnb.com/rooms/19010312 : $432
14 nights in Milan + Air fare for <$1,000.
Eat in the AirBnb for, what, $25/day? and you've spent under $1,500.