TALK ABOUT WEAPONIZING the First Amendment.On Wednesday, a Texas company called Defense Distributed planned to publish blueprints for plastic guns, until last-minute lawsuits aimed at stopping them succeeded late Tuesday. With those plans, which were already posted online and downloaded by thousands, anyone could theoretically make their own undetectable, untraceable firearm with a 3-D printer.The company argued that it had a free-speech right to publish the designs. It may be right: It’s legal to publish guides on how to build homemade bombs.Make-your-own designs for conventional guns have also been published for hobbyists. And Defense Distributed’s weapons are apparently not sophisticated enough to be covered by restrictions on sharing military technology; the State Department told CNN that the designs do not “offer a critical military or intelligence advantage to the United States.”Get in your inbox:Michael Cohen's no-holds-barred look at the absurdities of this political moment.Thank you for signing up! Sign up for more newsletters hereLegal or not, though, Congress should make it clear that actually producing a plastic weapon from the downloads would be illegal — just as using a bomb recipe from “The Anarchist Cookbook” is illegal too.That’s already the thrust of current law, the Undetectable Firearms Act, which prohibits guns that don’t trigger metal detectors. The law, though, doesn’t unambiguously cover 3-D-printed plastic guns. Democrats in both the House and Senate have introduced legislation that would clearly ban them.In the meantime, companies that lease 3-D printers should also be on guard and take steps to ensure their technology isn’t used for munitions, just as fertilizer dealers launched a program after the Oklahoma City bombing to keep eyes peeled for the next Timothy McVeigh. Sharing blueprints for 3-D guns may be legal, but that doesn’t mean it shouldn’t be as difficult as possible to put those plans to use.Even if the downloads go live on Wednesday, a surge of plastic guns is unlikely — at least, not in the United States. Sadly, ordinary guns are so cheap and easy to buy, including untraceable weapons on the black market, that there would be little point. With current technology, making plastic guns is expensive, and the weapons — made from the same material as LEGO blocks — usually fall apart after a few uses.But technology tends to get only better over time, and the time for Congress to react to evolving threats is now. Undetectable plastic guns have moved from concept to reality, and our laws need to keep pace.