then you could supply an army with plastic guns easily !
Not completely. The makerbot is a commercial version of the reprap, and the .stl (CAD) files for the plastic parts of those are still available, and the traditional first project for a new printer is a full set of the plastic parts to either have as spares or give to someone to get them started. You would still need to supply the guide rods, lead screws, belts/pulleys, stepper motors, heaters, tips control circuits and miscellaneous hardware. With careful scrounging you could probably build one for under $500. The problem with self replicating 3d printers is that the plastics aren't strong or smooth enough for the rods and screws, and no one has figured out how to print motors and electronics yet.