Look how succesful Guild wars, WOW and just about every MMO out there. Because you have to be online to play the game, piracy is less apparent. Yes its a online game but no harm in having that ability on a single player game too.
There is a HUGE harm in having that on a single player game.
1. If their server is down, if the company goes under, if they decide they no longer wish to support that server in 5 years, you cannot play your game that cost $50.
2. If I cannot afford to or do not wish to have internet then I can no longer play my single player game, which is unacceptable.
I understand looking towards the solution of log in system, but it does have its flaws. Single player games should not suffer from corporate failure. What if you wanted to load up Duke Nukem from back in the day but it required you to log in? I think youd be having trouble doing so right now.