I am going to have to strongly and respectfully disagree with you sir.
You can read several studies about the pros and cons of playing games. One particular article I remember reading says that games improve "rapid eye movement" and I think that could benefit us greatly as real life shooters. For example, if you are shooting moving targets, or needing to identify a single target in a group quickly.
Study: Video games can improve your vision <--- Linky
Not the original article I read but same general idea. Vision is only one way they are beneficial. I firmly believe that playing FPS games increases your reaction time as well as "quick thinking".
If you believe it, that's all that matters. Good luck to ya.