They will pass a law to put the genie back in the bottle.
They may try. We will oppose them.
I understand that one legislature once repealed the law of gravity.
[ They will pass a law to put the genie back in the bottle. ]
You can’t rebottle a Genie, not without burning all the surrounding villages and villagers...
It probably wouldn't work, at least not without voluntary compliance.
As an instructive parallel, take the case of printers, scanners, copiers, etc. The government leaned on the manufacturers to include intelligence so that the devices could determine if you were trying to print currency, and the manufacturers cooperated. If you try to copy a bill, the copier will give you an error message (and probably call the cops these days).
The situation is somewhat different with 3D printers. The government might be able to repeat the same persuasion they did with the printer and copier makers (though recognizing a gun part must be orders of magnitude harder than recognizing currency). In contrast with printers and copiers, though, 3D printers have become popular in the "maker" culture (cross a nerd and a gearhead and you get a maker). Not just using them, but building them, and there are numerous open source designs for DIY 3D printers. In fact the name for one of them "Reprap", is based on the fact that it can print the critical parts to spawn a copy of itself. This is going to be a hard genie to contain. How are they going to force nanny-code into a DIY printer?
With laws as they stand today, there's another obstacle for the rights controllers. Unlike the anti-counterfeiting provisions, they'd be outlawing specific technology out of fear that it would be used to engage in a LEGAL activity. While I'd be hard pressed to think of a legitimate reason to copy a sawbuck, building your own firearms by traditional methods is perfectly legal, so how do you justify criminalizing using a new tech to do something that's already legal?