Because you pass a BC doesn't mean we should undo the ban on new machine guns being manufactured. Nor letting the states decide on new MG's.
Since machine guns are heavily regulated for civilians, there's really not a large market for new ones- they're manufactured for the military, then the surplus are sold to qualified dealers who then sell to qualified buyers. Parts, OTOH, are less restricted and some are required to have a serial number that can be traced and is illegal to remove- the accessory parts like stocks, sights, scopes , etc are like car parts- they don't change the essence of the gun.
Who said we should undo the ban on machine guns (assuming fully-automatic)? Firearm manufacturing and sales are regulated on a Federal level, not state by state but concealed carry permits are restricted in some places, with or without reciprocity and some states don't allow that, at all.
But again, if you look at crime reports, you'll see a lot of felons in possession of guns because they just can't be bothered to obey the existing laws.
I understand hating the idea or fact of gun availability because I have known far too many people who used them to end their own lives, a few who were killed and the neighbor who was shot in the armed robbery attempt but I can't understand the idea that people should be defenseless. I don't mean they should constantly be paranoid- as I have posted, if someone is always in danger, they're in the wrong place. However, armed robbery comes in many forms & people, like business owners who are trying to make a bank deposit or sell expensive items that can be sold easily are more likely to be robbed than most and no, their insurance company won't just hand over the payment without a lot of questions. Also, the robber(s) won't always ask for it peacefully.
Nobody should need a gun- people should be able to live in peace but that's not reality. People do stupid and dangerous things every minute of every day in every part of the country. The rest of the World can take care of themselves, but this country isn't under the control of any other, nor should it be but people from other countries shouldn't be attacked by anyone in this country, either. That goes for other places too, but foreigners are attacked everywhere, so the problem isn't unique to the US.
The root of the problem is people doing terrible things and not caring about laws, people, property rights, etc. What they do, use and how they use it is up to them but it's hard to stop them. Complete gun control, by nature, restricts people who aren't criminals and that won't be good for anyone because there's no way to guarantee that if all guns are to be confiscated, they'll ALL be turned in or handed over.