To preempt what I imagine will be a response to this question, which is that these users are violating the TOS with Airbnb, I have two points: the first is that Airbnb itself is violating many "TOSs" - laws - so it doesn't give them very good moral standing here.
The second point is stronger (I think), which is that Airbnb's position here is logically inconsistent. They either believe strongly that you should be able to do what you want with the properties you own, or you don't. I simply don't see why it matters if N=1 or N=10 (put differently, N=1 is not a special case that deserves being considered differently).