It's a landlord problem if it happens in one place. If it's happening all over the place and is facilitated by a single entity or a small number of entities, it certainly is a problem that will end up getting solved by legislation.

If AirBnB were serious about legal compliance, there are plenty of tools they could make. Any developer here could suggest several, I'm sure. But they're intentionally sailing very close to the wind. They've done well by it so far, but I could imagine this strategy biting them in the ass if they push it too far. A couple of spectacular failures yielding some dramatically written articles would be enough to generate a lot of public outrage.