So he's right? Every response on this thread seems to be ad hominem. No one seems to be defending AirBNB guys. It is relevant because any online business necessarily has a lot of information about its customers. Spamming is both illegal and immoral (free riding on the commons), so I would choose not to give my business/info to people with a known history of such activity.
Also, spamming may be against many company's TOS but that does not make it illegal.
Go read the CAN-SPAM Act.