Firstly, is this a new game? I played Modern Warfare 4 months ago, and you're telling me MW 2 just came out?

Secondly, I don't believe in censorship of video games. So what if the video game allows mass murder? So what if it allows worse things? 

As long as it's regulated to have clear markings on the game box, it's up to the publishers if they want to publish it, the distributors if they want to distribute it, the stores if they want to sell it, the parents if they want to buy them or let their kids buy them, and the gamers themselves if they want to play them.

I look at it from a principle of harm and benefit more than anything. I've not yet seen any evidence that video games has any negative effect on the adult mind - Of course, even correlation doesn't imply causation, either. If there is any significant negative effect of violent video games (when played above the often outrageously high age limit), then we have a conversation.

Until then, even granting that some games promote violence, which is a fairly defensive argument, I don't think that's enough to warrant censorship, even if it's distasteful. If you're promoting violence against a certain group in real life, then we have an issue because that is potentially hate speech, in a sense. Promoting general mayhem is something else, which is why you can make movies about death and rape and torture.

As for my personal choices, I don't think I will be buying Modern Warfare 2, and this thread hasn't helped the game in my perception.

Keep in mind that "playing the bad guy", or just the option to do so, is extremely common in computer games. Regardless if the bad guy is an assassin, a gangster, or an American soldier in the Vietnam or Iraq wars. Realism has upsides and downsides. One downside is that reality itself is not always very nice. That's why we need computer games, movies, and literature showing us the horror of war and violence. If you pretend violence doesn't exist, you're just promoting the spread of it.