It used to be possible using the Facebook API to loop through all of the content on pages for users, posts , comments and all of the associated media. IT was not very difficult if you knew what you were doing. This been shut down for obvious reasons. So what is a dataminer to do if he or she wants to grab some posts.
There is a work around. You can hookup python and clone various projects from git that use python facebook-scraper Facebook Scraper
Some of the projects listed on the page work well with only minor mods. Kind of fun and potentially usefull for machine learning projects.