Comparing gamers to drunk drivers is not only ludicrous, it's offensive. Just because someone plays and enjoys video games doesn't mean they aren't smart enough to be objective.
As for the subject itself, using video games for training is impossible. As a US veteran and a gamer, I can say with some certainty that aiming with two thumbsticks and some buttons is a lot different than aiming with a weapon. I know several people who are great at Call of Duty, but give them a rifle, and they couldn't hit the ocean if they were standing on the beach.
Desensitizing? Perhaps. But no more than the news anchor who reports on a school shooting, then perks up 30 seconds later to tell you about your favorite sports team.
People are most frightened by that which they do not understand. And frightened people have been trying to find a reason people do these horrendous things for years. Before video games it was Ozzy Osbourne. Before Ozzy, it was Elvis. For some reason, people can't grasp the fact that someone else's brain is wired differently than theirs.
It really is that simple.