No one big country goes and kills the other big country so openly. Every politician, even a 5th grade one would know of it.
Because wars are two sided and today's warfare would cause massive loss of resources even for the attacker.
Therefore, in reality, if such a terror act happened like the one in game, a "similar" act would've been done to give the same impression that "we can do it as well" kinda.
Yes, killing civilians and all that stuff is very bad and dark for people like you and me however its a statistical number for a leadership.
It is why that game's story fails. And it actually shows the American's not as bad guys but wrongly framed guys, it shows one particular guy bad who has some power.
Its a different thing. Actually that was as disturbing as seeing that epic fail story. Showing one side as good other one as bad or unknown is lame and disturbing in "political flavoured" games/movies. However, I wouldn't expect anything else from Infinity Ward, especially after I saw the "Special Thanks to US Army" line at the credits.
American people -> Don't get this wrong, I am criticising the game. Not someone else's patriotism or favorism. Game is not only sold in US and its rather a cheap propaganda. If you will do it, at least do it with style is what I always believe.