There's an awful lot of current and former military at the range I usually play at. I'm neither, but I rather enjoy shooting people and not going to jail for it.
As far as people "pretending to be something they're not," well, I guess by your logic nobody should ever play a game of basketball, baseball, or football unless they're in the NBA, MLB, or NFL. After all, they're not "real" players, right?
As others have mentioned, it's good for tactics and teambuilding. It's also a hell of a lot of fun. A thing does not have to have practical purpose to still be valuable.