Because it's extremely ignorant. For every person like this there's 3 million that understand, and process, the difference between reality and video games. I played Doom and Wolfenstein when I was five, played Medal of Honor when I was 10, and currently play COD and Halo while I'm 24.
Why don't we demonize movies, books, music and every other form of entertainment while we're at it?
Regardless, no need for debate at a time like this. Just sickening.
Just to play Devil's Advocate, the graphics on the games you played during your formative years were way less realistic than they are now.