my chat with support...
>>> I hope this helps answer the question for everyone. I still don't know what the "add to my Mac" option would have done but here you are...
It looks like recent updates have removed contact syncing between macOS/iOS and FaceBook. This seems to have been done because most people don’t keep in contact with all of their FaceBook friends, and syncing this causes clutter.
From here, we can choose whether we want to sync (add) the contacts to iCloud, and thus have them on any devices of yours syncing with iCloud, or to not have your FaceBook contacts sync with your devices.
The delete option would keep them on FaceBook, but remove them any FaceBook contacts from the device.
It may be that you had added the account previously, but not set up contact sync. If you didn’t have the FaceBook contacts listed in the Contacts app, that would be my expectation.
>>> I had no connection established between fb and anything on my mac except the safari keychain
>>> I chose delete and noticed no change to my contacts.
>>>> I asked the tech person to let the developers know this was a problem and that the wording was not sufficient.
Fantastic! I’m glad we were able to sort that out. I’m not personally able to contact the developers, but I definitely agree that was a frightening way to put it!
The great thing about Apple products is the continuing improvement that we seek for our customers. We offer a feedback page that allows customers to submit suggestion directly to the promotional teams that you can view at http://www.apple.com/feedback . They read all feedback and consider them when implementing future software, products, updates and promotions.
