If there's actually a concrete claim you want to make, something more precise like "copyright infringement" or "violating the license agreement" is probably better. If you aren't accusing them of anything in particular but wish to express disapproval, it would be best just to call it "morally wrong" — though I don't think that would make for a very productive discussion.

"Piracy" is a political term used generically to mean "people not doing what I want who should be made to obey me by force of law." It may refer to actually harmful illegal acts (bootlegging) or things that are simply not preferable for somebody's business model (watching legally obtained content on an "unauthorized" device).