Definitely not all strategic communications could be detected and blocked. However some research has been tasked on the issue. Take "Antisocial Behavior in Online Discussion Communities" (
http://arxiv.org/pdf/1504.00680v1.pdf). This paper, though it terms it 'antisocial', studies online influence operations and is mentioned on NATO's propaganda ("strategic communication") centre for excellence Facebook page (
https://www.facebook.com/StratComCOE).
The point of having a rule set that can be pushed to like the system described here is that it can be fed information from a centralized task force. Indeed, these systems are used across industries with patterns and rules to detect malware, hacking, and a host of other activity (using formats such as STIX or TAXI).
It's unlikely that Facebook itself would be trying to determine whether a post to some content is propaganda - it's more likely that their automated system will apply the rules it receives from information defense agencies.
As per your other note, the selective censorship of information is absolutely a form a propaganda of its own. Facebook (and the US government) don't have the best history here and have 100% certifiably censored information to prevent effective organization of (for example) May Day protests. I'm not going to go speak about that at length here - hoping to get some technical clarity from those involved.