"So, to get these perceptions, we’ll share Airbnb profile photos and the first names associated with them with an independent partner that’s not part of Airbnb. "

I have to imagine they considered making this opt-in and realized the vast majority of users wouldn't take action to increase sharing of their personal data. Despite the good cause, it is incredibly shady that they would implement this as an opt-out.

IANAL, but I would think that this would be a flagrant violation of privacy laws in many regions outside the US (this policy is limited to US hosts and guests).

Edit: I also did not receive an email, but found the toggle active in my account preferences after reading this post.