Yes, but without it sales would still be huge

No they didn't. We have been acting as "terrorists" in many a game before MW2 came out, it's just an incredibly popular game so it got more media attention.

What plot? >_> (and yes, I've played the game)

The plot is about some idiotic decisions causing Russians to invade America.  Shephard betrays you and planned it all so he could be remembered as a hero.  The story makes very little sense, the fast pacing didn't help much.  IW has always done a better job at making exciting set pieces than telling a good story.

That level just gave you the feel for Makarov and how intense he is. They wanted you to see first hand his power and what he can do. That is the reason for the level.

It fit the story perfectly, it wasn't for publicity.
People need to realize the story is about some crazy terrorist, what do you expect?
Him to give little kids candy?

So you're saying that Modern Warfare 2 sold over 8 million first week off hype alone?

Puh-lease, cut that crap. It still would have sold million of copies, but let's not act like the advertising and the controversy didn't help a bunch. Companies wouldn't advertise if it did nothing.

how about it was an essential part of the story?

I don't why the level is there to be honest. But then, I'm of the opinion the entire SP campaign structure and narrative is awful. Good action, but terrible, terrible narrative.

The level itself simply doesn't work for me. I don't see why they'd go for cheap publicity, and maybe IW really feel they were trying something risky - but personally, as someone well educated and versed on literature and cinema and narrative devices, I have to say they didn't really make it work.

Also, having a cheap gag right in the middle of the level undermines totally any argument for depth or a serious attempt to convey something shocking in the narrative.

But then this is a game that imagines Russia would invade America after a terrorist attack where an undercover American was shot by his own accomplices after the attack - i.e. it's simply not really worth expending energy trying to take it's plot and narrative seriously in the least.

"Remember... no Russian..."
How are we supposed to make the difference anyway ?