Well yes, but that doesn’t affect people who plan to murder with them of course, the added time for doing it with a “machine gun” specifically is nothing compared to already getting life, the death penalty, shot by cops, or suicide at the end of their spree killing.

Though no, guns are legal to print, the switch is defined as a machine gun by the ATF and that is illegal without the proper licensure. You can print a glock no problem, but you can’t sell it or make it full auto.

Most guns used in crimes were indeed initially purchased legally, but then stolen or sold illegally through a process called “straw purchasing.” The ATF reports avg “time to crime” (from buying in-store until found at a crime scene) of guns they find is 11 years and the overwhelming majority were straw purchased. Now, it’s important to note that this isn’t to say that most guns bought have 11yr before a crime happens, rather that most guns involved in crime (which is a fraction of a percent of all guns sold/owned) took 11yr to get there.