The inability to use online multiplayer unless you are the original purchaser is pretty ludicrous. Video game companies claim that they lose money by consumers purchasing used games. This may be true to some extent, but those used games had to be purchased new at some point. And what about games that have been out of print for long periods of time? Why should I be penalized for that?
To be fair to Mass Effect 2, however, the "Cerberus Network" registration code that you receive with an original game copy only gives you three free DLC packs; it does not break half the game as Sony does in TFA. You can still play ME2 without registering the game; you simply do not have access to DLC (most of which has sucked thus far). It remains to be seen if purchasing DLC requires registration.
Save the whales. Collect the whole set.