Yes, the laws serve a distinct purpose and they do it very well. It's fine if you want to own a handgun for protection purposes, or a rifle/shotgun for hunting, but who really needs to own a fully automatic, military-grade assault rifle? It's not something the average person needs or should have, because in the wrong hands it could very easily turn into a massacre.
I don't see a problem with having civilian versions of common military weapons. Even in sport, there is no need to have a fully automatic M16 or something. Hell, even in a real combat situation, going full automatic is a foolish thing to do in the first place. It just wastes ammo and makes you more inaccurate.. that's why a lot of the time they're using semi/burst fire modes. Self defense is self defense, you shouldn't have to unload 30 rounds into a dude to defend yourself.