legally the data is not public and the fact that facebook is actively trying to prevent scraping is making it very difficult to argue otherwise.

Legally, the data cnanot be public. The users give facebook a non-exclusive license with limited rights to store and process the data. From this does not follow the right that anyone who sees the shared images (for example) has a right to process them as well. If that wasthe case, the terms (https://www.facebook.com/terms.php 3.1) would have to state under which license the works are redistributed by facebook.