Are you basing that comment on the CNN report? Or first-hand knowledge of the game?
I don't have any first-hand knowledge of the game, but I do have first-hand knowledge of CNN's track record of distortion. Also, I read the Left Behind series and it certainly does not advocate Christians killing people.
Here's a balanced review of the game, by folks who played it for over 40 hours: http://www.pluggedinonline.com/thisweekonly/a0002989.cfm
Oh, no, I'd take any report on this subject by CNN as dubious at best. I saw a review of the game (just that, not on the book series) on our local newscast and wasn't terribly enamored of it. The convert or kill claim sounded more like a game at Islamofascists... of course, they don't need a computer game to do something they practice doing for real.