We need to undergo training to use a potentially dangerous power tool on a construction site. We need driving lessons before we can drive a car. Given how dangerous guns are, it only seems right that we should have training for those too.
Teaching gun owners the best practices surrounding gun ownership, like checking the firearm to see if it is loaded, keeping one's finger off the trigger until you intend to shoot, and safe storage practices would significantly reduce gun-related accidents and prevent accidental discharges. It would also keep the Second Amendment intact. Switzerland has a stringent firearm training programme and, correspondingly, a far lower rate of gun deaths than the US.
It would violate the Second Amendment by imposing economic restrictions. Not many people can afford a $100+ training course. If the government makes these course a mandatory part of gun ownership, it would only be the middle-class and the wealthy that would purchase guns. This is against the spirit of the Second Amendment.
Individual rights are not unassailable. Only certain people can be trusted with certain rights.
[P1] In other industries we make training obligatory for reasons of safety. [P2] Guns are dangerous. [P3] They should only be available to those with training.
Rejecting the premises
[Rejecting P3] This would amount to a violation of the Second Amendment.
Rudolph, Kara E., et al. “Association Between Connecticut’s Permit-to-Purchase Handgun Law and Homicides.” American Journal of Public Health, vol. 105, no. 8, 2015, pp. 49–54. Crossref, doi:10.2105/ajph.2015.302703.