I really should have but my point (a) and (c) together. The legislature and courts have already ruled that there can be limitations on the firepower citizens may own, so somewhere between musket and artillery a line is drawn. I'm simply arguing that this line was not drawn by the constitution, it is drawn by current political conditions, and by the same logic there is no reason it couldn't be pushed closer to the musket end of the spectrum. Furthermore, I don't believe the 2nd amendment in any way prevents requirements for background checks, training, licensing and registries. In fact I think those would fall perfectly under making a militia "well regulated".