That's a very unfortunate situation: being an Airbnb host, from some point of time I started receiving messages with other guests for listings that I have no relation to.
From one side, I can simply ignore it, but from another - who can guarantee that communications with my guests for my listings don't go to other users?...
Having created a support case in Airbnb, I simply got a message that it'll be addressed within 24 hours, irrespective that I indicated that it's a breach of confidentiality.
So, being a host or a guest, please be careful with information you circulate in the Airbnb messages. "Better to be safe than sorry" as an old proverb says
We do as well, yet sometimes guests share their contacts, or passport data that we need for guests registration. I personally believe confidentiality shall be one of the top priorities...
@Alex1628I don't see any issues with the passport and contact information sent in Airbnb message app. It is supposed to be Airbnb's responsibility to keep these messages secure and confidential.
As hosts, we just make sure that we don't give those info outside of Airbnb message app.