Well if you think it's beyond good taste, don't pull the trigger (push the X or whatever button). Just watch the baddies mow them down. I don't think it's beyond bad taste.
Now raping an indian woman who is tied to a pole while dodging volleys of arrows is beyond good taste.
Well everyone is going to have an opinion on what they'll find acceptable.
Unlike the GTA games where you were presented with the freedom to do what you want (and yes all the GTA games are very tongue in cheek) this missions objective is just to murder civilians. In the same style I might add as the Mumbai attacks in 2008 when 2 people with AK47's walked into a packed train terminal and murdered 50+ people.
I personally think that for a game of this type, with the original MW fanbase (let's face it, CoD4 has a massive <18 fanbase) - that this is an irresponsible thing to allow the player to control.
Even if you can skip it - how many 12 year olds do you think whose parents are too ****ing stupid to know better are going to skip it?
There are enough douchebags looking to strip down/censor/ban games already and this is perfect ammunition for them. The last thing the industry needs is more regulatory oversight or scrutiny.
The only thing this is good for is generating publicity through outrage. It's a stupid cheap marketing tool that'll could have ramifications for an entire industry in the stricter countries (Germany/Oz spring to mind).
And as for "It's just a game" - surely you must realise that is no longer a valid argument for anything. Games haven't been "just games" for at least the last decade.
They are a dynamic and exciting form of entertainment, and a form of art. More games are sold in a year than films, and whether they have artisitc, pedagogic or purely entertainment merits - when something has garnered such a massive popular appeal it is no longer "just" anything.