(1) How many people today actually make their own guns? How many people make their own drugs? I'm pretty sure that ratio has a lot to do with the relative difficulty of making a gun vs buying it and the difficulty of growing several different drugs vs buying it. Yet people still buy drugs. Alcohol is one of the easiest things to make, and people still bought it; that probably has a lot to do with their consumption level and generally the social aspect of it. Maybe if there were more gun clubs and we were talking about bullets...
(2) Which leads to, we could just heavily tax bullets. I'm sure people would be just as upset with that, but we do heavily tax alcohol. I guess it's okay to consider it a vice to make yourself sick with alcohol but not to fire bullets that may injure yourself or someone else.
(3) There's an argument that all the effort to make a gun with a CNC machine would be enough to motivate people to not go around killing people precisely because part of the basis for mass shootings is not merely a hot blooded desire to kill--which is generally the argument for removing easy access to guns reducing murder by guns--but a more long-term feeling of worthlessness. If you can make a gun. or really all sorts of things. with a CNC machines, suddenly you realize you have value in life, and you're probably less inclined to throw it all away on some path of self-destruction. One could even argue, funny enough, that drug addicts could be trained on CNC machines which will give them the skills to make guns.
In any case, the thing about CNC machines and 3D printers isn't if they can fire a bullet or two. It's whether they can fire dozens before the gun jams or worse. Realistically, it's a non-trivial thing to build a sub-machine gun or machine gun, even if building a simple gun is within the realm of doable.
PS - If you would like to guess why drug addicts who grow drugs don't in their act of gardening (or chemistry) potentially overcome their addiction by a realization of their own self-worth, I'd note that growing/making certain drugs is so trivially easy that it's really hard to convince someone they've done anything special. Also, drug addicts are taking drugs. They almost all have a profound psychological effect on the person taking them. I guess one could say the same thing about people buying a gun, but that person is on the opposite end--they derive their self-worth because they bought a gun. I'd say that's more pathetic than being a drug addict.
