GamePro.com's interview with Jesse Stern (who has a day job as a writer for the NCIS TV series) has him talking extensively about that airport level, where Russian terrorists mow down unarmed civilians. He states, "Every single person in testing opened fire on the crowd, which is human nature." He adds, "I hope that people don't just look at it as being this simplistic and brutal sequence. We've done our best to treat it with care and not to make it gratuitous."
Ultimately Stern feels that the sequence was worth putting into the final product, saying, "This is a triple-A game and the top grosser of all time with this huge budget behind it, yet we're still taking major chances wherever we can and the airport level was a risk we had to take. Sometimes you take huge risks and it really works. Sometimes it doesn't work at all. But if you don't take the chance, you're not going to make something new."
Gallery: Modern Warfare 2 Screenshots