I am a huge fan of academia.edu. I have been promoting it here on AWOL since it was a new service five years ago. It has exploded since then, without any apparent adverse consequenses. I reached my limit of two thousand connections long ago. I've communicated my feeling that limiting any individual's network to two thousand connections is a silly and counter-productive limitation, but they don't listen to me. What that means is that I am limited to seeing the activity of early adopters, or dropping connections to people I'd like to be connected to in order to connect to others. In practical terms it means I don't visit the site very much, but depend on the push notifications sent when those to whom I am connected upload their scholarship to their profile. And those push notifications are extraordinarily rich! What I see among them more and more of are the full-text facsimiles of articles and books published by commercial publishers. To all appearances, most of these are violations of the copyright agreements signed by the authors with their publishers. In the few cases with which I have some personal connection, the responses by the author to a takedown notice is along the lines of "oh, sorry, I never read the text of the publishing contracts I sign, I just wanted to share". Sharing is good!
But more and more of these things are from Brill, De Gruyter, Oxford, Cambridge, Springer, Eisenbrauns, Fabrizio Serra, and so on: the core of commercial publication in ancient studies. Despite the fact that ancient studies is seriously small beer in the world of publishing, there are jobs and companies at stake here. It won't be long before these firms take action against academia.edu for their (perhaps passive) complicity in the copyright violation. Then what. Will they fold? How would that be good for you and me?
But here's the real question. I presume those of you who make your scholarship available in open access on academia.edu do so because you with it to be seen and read by the widest possible audience, possibly informed by an understanding of principles of open access espoused and promulgated by a variety of national and international organizations. If this is the case why not publish in born digital open access publications in the first place? Is it prestige? Never mind, your work is good, their editors are good, prestige follows your work and their editorial control. But really, support the open access journals. AWOL's full List of Open Access Journals in Ancient Studies lists 1382 titles today. Find one you like, submit your article. Do it!