I see how it may seem like facebook is parasite project in a scenario of using facebook that is most common (sharing photos, liking, tagging pictures, having friends,..). But users that use facebook platform like that are all doing it by their consent. If user chooses to do so it may leave the platform at any time.

While in parasitic relationship there is one side that is being parasited without consent and other that is parasite. If we must compare facebook and its most common users with realtionship in nature it is more like symbiotic relationship.