There are various little handbooks of the "Citizen's Guide" variety which have the Declaration of Independence, the Constitution and the Bill of Rights. And, commonly, other stuff about the philosophy of our laws.
Anyhow, many of them include the Preamble to the Bill of Rights. That gives the purpose of the BOR: To avoid abuse of power by the state.
IMO, that alone should make it obvious that the Bill of Rights is a package of restrictions upon the government. You can't have it both ways; a set of restrictions upon the government cannot at the same time be a set of restrictions upon the people as individuals or the people as a whole.
Further: The same few people wrote all ten amendments. They were noted for scholarly consistency in their usage of words. Thus "the people" cannot be single in one amendment, and plural in another. That just does not make sense.
My personal opinion is that focussing on such things as "What is a militia?" merely shows that folks lost sight of the fundamental reason for the total package that is the Bill of Rights. Bogged down in secondary issues, unless it's carried back to how militias were actually organized in the late 1700s.
Art