The second amendment is about ensuring you have a body of men that know how to use weapons, that you can call up in defense of the country. That's what it's for, all right there in the first half of the text, up to the comma.

"being necessary for the security of a free state" isn't high-minded idealistic philosophy on the nature of the individual human, it's meaning "to keep our country safe from those Europeans over there, should they come a-knocking". Instead of "it's there so our government will fear us", it's "it's there so our government can call on us, and we will have the right skills to serve".