airplane restrictions

I was reading the Transportation Security Administrations guide to what is and isn't allowed on airplanes nowadays. Of course, you are not allowed to carry on or check guns. Duh, right? But, and I do repeat but, you are allowed to check, in your luggage, parts of guns and other firearms. Am I the only one that's ever heard of people who can assemble and dissasemble a gun from parts. SO you can't carry a functional firearm or check it in your luggage, but you can check all of the pieces and put them together when you get where you're going. How fucked up is that.