Stopping piracy entirely is nigh impossible. DRM and always online games do however provide a deterrence against piracy and cheating. That alone is pretty much a fact. May deter a little or a lot but its a deterrence none the less.
I simply have issues when a game is not designed around multiplayer yet hinders consumers with unnecessary DRM. It may reduce loss for the pirates but the cost against players simply outweigh it. Single player requiring online connection is practically an oxymoron.
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Steam is also a form of DRM.