No it’s not, it’s a bullshit excuse to do nothing.
If your goal is to feel good about Doing Something then you are right. If the goal is to meaningfully reduce violence without curtailing the rights of law abiding citizens, you are dead wrong. The only effective way to go about this is to logically look at what the effect of a law would be.
Overwhelmingly, criminals, abusers and domestic terrorists are using legally purchased firearms to kill innocent people. Of the minority remaining that are using illegal firearms, they were stolen from somewhere and those people should be held accountable.
First of all, you are mistaken here. Guns used by criminal groups are most often straw purchases, which are very much illegal.
More importantly, looking at the problematic people and just banning whatever they have in their hands has a long history of failing to make any meaningful impact on crime.
As an example, let’s examine the long list of weapons banned in CA after the legislature associated them with “gang activity”. Martial arts tools like nunchucks, which have no practical use outside training, were banned, despite the fact that it should have been patently obvious that banning nunchucks would do zero to stop actual criminal activity.
Another example is prohibition. People saw the “immoral element” consuming alcohol and saw alcohol prohibition as a panacea. It’s well known that prohibition had wide sweeping negative effects at this point.
You have to predict the holistic effects of the law, long term, to see if it will have a positive impact.
“Oh but what about 3D printed guns and bombs and cars? They’ll just use them instead” doesn’t matter. They’re not using 3D printed guns any more than they’re using giant clown hammers.
… it kinda does
It’s not just a “what if” question, either. Even prior to the advent of readily available 3d printing, criminals in Brazil and elsewhere had developed a network of facilities manufacturing black market open bolt sub machine guns based on the Luty designs. Restricting legal guns had little long term benefit in Brazil at stopping crime with firearms.
It has only gotten easier to make them at home as time goes on. No manufacturing facilities needed.