Seems we have a case of a rather flimsy argument here. If you are to post a contravertial thread its very important to get your wording right, "poisoning video games image" is very different to "diluting the industry" to "being too popular and therefore overshadowing lesser known titles" all of which have been mentioned in this thread. So, to put it to rest, lets examine each one of these things in turn.
1. To say it Call of Duty as a franchise is posioning video game's image seems a bit odd, since for the most part its shooting nazis, and when its not shooting nazis its shooting terrorists. Nazis and terrorists have long since been the bedrock of things to kill in both video games and films so this holds little weight.
If we are to say that it gives the impression that "every gamer is a Call of Duty fan" yes this can often seem the case from the outside, simply because its the most sucessful franchise at present, what with MW2 breaking various records. Though, not too long ago a little game called Halo came out on the Xbox and as I recall, every gamer was a Halo fan, right up until 3 which is still the (2nd?) most played xbox 360 game out there.
2. "diluting the industry" is perhaps a more relevant reason, and one I do agree with to an extent. Due to Modern Warfare's vast pulsating popularity it has meant that in an effort to make a near-popular game other game designers have made modern wafare-esq games with their own little twist. Nothing so in your face as modern guns/terrorists (though there are some, Bad Company 2's single player for instance) but in more subtle ways: regenerative jam on your face, fast and light character though still claiming "realism". That last one is probably a little unfair no one ever complained that Unreal runs along at 100 miles an hour with a pin point accuracy zero recoil rocket launcher

but I love it. However, the hide behind a box until you wipe the jam off your face is par for the course, rendering many games rather... unimaginative, so this I will grant you.
Addendum: There is a reason for this however, its because its good fun. Popular things are popular for a reason. If it works, why not emulate it? why not make a hundred games with higher and higher production values because no one ever gets tired of *boom headshot!*
I digress... Tremble puny earthlings soon my mighty race will destory you all! *ahem* sorry.
3. I have already covered popularity so I will just touch on overshadowing. The games industry is so huge and diverse I don't really think this is the case. Bad Company 2 is a superb game, and its never difficult to find a server to play multiplayer. So does it really matter if everyone around you prefers MW? Its a different experience. If your friends don't want to try BF, that's their problem, all you can do is ask them to consider an alternate game. You must not fall into their ways of thinking, "Bad Company is superior, MW2 is rubbish!! because this makes you as bad as them. Further, considering the slew of FPS on the horizon, it doesnt look like Call of Duty is dominating at all. F3AR is around the corner and Crysis 2, both excellent long standing series. Halo Reach of course, then a new IP, Rage which has dominated critics attentions at E3 overshadowing even Black Ops. Infact, though it is clear Black Ops is a quality title, it has become so obvious that the Call of Duty franchise makes decent games that it is past over and the attention firmly placed in the fresh and the new. Call of Duty: Modern Warfare 2 is a fad, and one that will be passed over by the next big franchise with mass appeal.
My own 2 pence: I think this problem, and infact this thread is symptomatic of the problem, is that mass appeal means that a franchise is scrutinised. Look at Halo, once the bees knees, now mostly shunned and complained about since its the done thing. (note people still play it ALOT so this argument is thin also) Anything with mass appeal with have the lovers, of which there are many, and the haters which are less but louder - it is the way of things. Mass Effect 2, the lovers, and the haters who say its not as good as the first. Dead Space, the lovers who thought that the action horror was visceral and terrifying and the haters who found it wooden and not scary atall since you could cut up the badies no trouble. (The old its not scary if you're competant argument)
So play the games you love, moan about how rubbish everyone else's taste is if its not yours and the world will go on as before.
Also, woo 100th post. *birthday poppers*