Seriously speaking, if Activision went through with this, they would lose so much revenue in a flash. People wouldn't stand for it, and it is guaranteed that the number of people subscribing would be at a very low level. There'd be a fair few desperate and 'hardcore' CoD players who would pay, but most won't. And the sad fact is, if one company does it, then others will potentially follow suit. It could see the potential end of multiplayer gaming as we know it, or a lot of gamers out of pocket for a while. Either way, if Activision go for this, then the next few months will be a very tough time for online gamers.
For the record, I say no. Why should I have to pay extra per month to play a game I've already paid for at the shop, and pay monthly or yearly for anyway with XBL?