Here is a boilerplate you can copy/paste if you don’t want to opt out of the “Project Lighthouse” discrimination study, but only out of data sharing for marketing purposes:

Subject: Opt out of marketing for user <your-email>

Please do not use my information for any marketing purposes, and do not sell my information.

I am sending you this email based on your documented policy quoted below:

Please note that you may, at any time ask Airbnb to cease processing your data for these direct marketing purposes by sending an e-mail to opt-out@airbnb.com.