There are all kinds of 3D printers out there that you can build yourself so presumably the US Government would have to enforce the law itself if you were to print your own gun with one of those. What if you were talented enough to make your own guy out of steel or some other kind of metal?
People make "zip guns" (improvised, simple sing-e-shot guns) all the time; you can do it with a bit of steel pipe, a nail, some rubber bands, and a lot of ingenuity. It's way easier and cheaper than using a 3D printer to do it.
Yet, somehow, society hasn't fallen into anarchy and ruin.
I just really don't see 3D printed guns ever being a big deal. I mean, sure, Stratasys is entitled to reclaim its property if it wants to (my understanding is that he was using a loaner 3D printer for the project), but really? I just don't see hordes of people rushing out to...err, buy 3D printers and do the complex, fiddly work it takes to make a gun.
Tempest in a teacup, seems to me.