If you have a method of removing "Ghost kits" without the wholesale restriction of 3-d printers, more power to you.

That does seem to imply that enabling this technology now is premature, and maybe needs to be restricted. There is nothing inevitable about the introduction of a new technology into society. So far as I understand there's nothing in your constitution about a right to bear 3D printers...

Perhaps some technical solution could reduce this risk, so that any attempt to make an illegal weapon alerted the authorities, and the equipment would cease to function. In the meantime we can do without them, as we have till now. As you said, Bruce, and I agreed with you, liberty has its limits.
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Clearly there isn't going to be an overall ban on guns in the US in this age of society at least. Arguing about it either way is a bit irrelevant, and diverts people from addressing what you need to address. Far better to talk about things that could be done and whether they should be done, and how. To get them done.

There are plenty of ideas that sound very sensible - however it appears that the NRA is strongly opposing most of them, presenting sensible ideas as the thin end of the wedge". And also that in doing so it may not acting in accordance with what most gun owners actually wish. The first thing your sensible gun owners surely need to do is to take over the NRA.

I don't know about the USA, but where I live the organisations for drivers don’t campaign to abolish speed limits and driving tests and seat belts and annual checks on the safety of our vehicles. If they did members would seek to change that, where they didn’t transfer to other organisations with sensible people in charge.