Actually, it's not at all like sharing hard copies of a game. In fact, it's got some pretty heavy similarities to piracy.
Think of it this way - you purchase a Hard Copy of BF3. You can share the disk between friends, but you cannot readily create copies of the disk. This prevents a single disk from being used on multiple consoles or personal computers. If you were to copy that disk [ie rip it and share a .iso or other image file between pc's, along with a crack to allow the software to be used] then that'd be a form of piracy.
This is no different. You 'share' BF3 to four other people - that's four people who get free games and free content, and that's 240 USD in profits that EA and Dice are out. Add in another 50 per person for premium content, and that's 440 USD premium. As that counts up, that is an insane amount of profit loss created by the illegal transfer of unlicensed games. Piracy.
It's illegal, buddy, which is why Sony's had to crack down on the ability of PS3 users to 'share' games like this. If it keeps up, you can bet your bottom dollar that they'll either cut the feature entirely or face some nasty penalties from major publishers - EA, for example, isn't going to be as likely to put flagship titles on the PS3 if they think that piracy is going to chew into their profit margin by a significant percent.
It's the same reason why so many PC games have to be played online now - Origin games being a major example. Publishers don't like it when people share games for 'free', because it seriously hurts their profits.
tl;dr - this is illegal, and I'd be seriously surprised if an admin didn't lock this thread.
Giving someone a hard copy of your game implies that your friend can use your game but you cannot use that specific disk while he does. That's not illegal, as it's equivalent to renting. However, "sharing" game files (independently giving copies of the game while retaining the original) is. It's illegal to make copies of any game in any form without the expressed permission of the publisher. It's not thought about as much, but PS3 and 360 games are just as often pirated (if not more) as PC titles. It's actually much easier to pirate PS3 and 360 titles since they usually lack any sort of anti-piracy coding. This is why rented console games are getting slanted nowadays, since developers/publishers are adding benefits to those who buy the game new rather than used.
Sharing games in any form is illegal and we do not endorse illegal activity on the forums. Borrowing is completely different.