By this logic, you should also have to jump through those same hoops to get things that can be used to create with minimal experience said tools explicitly capable of sending projectiles at lethal speeds, or: this bill.
Sure, guns were "designed to kill people," but A) so were swords and bows/arrows but those are legal and B) self defense is not morally wrong. Just like your bag of sand, guns can be misused to kill people illegally, but that is still a misuse. Of course, nobody is even advocating for NICs checks for other weapons, nor harder-than-NICs measures like quiver size restrictions or "ban assault (compound) bows.."