I think your parenthetical expression is a bit more than just word-fluff entered by a founding father in a flurry of poetic inspiration. It clearly describes the intent of the amendment. People need to be armed to defend the state.
Actually, it says "being necessary to the security of a free state. You see, the guys who wrote this had just risen up against their government and created another in its place. "A free state" doesn't mean "The United States of America"; it refers to a fundamental concept. That concept is one of a place free of tyranny. The men who wrote the Second Amendment would have gladly overthrown the government established by the US Constitution had it become sufficiently oppressive and tyrannical. They would have done so in order to ensure the security of a free state and they would have done so with their own guns.
The US didn't have a big standing army at the time, and it was clear that to keep free, they would need to be able to call up their citizens if they were attacked, and those citizens better be armed. Given that the US currently has a larger army than the rest of the world combined, I don't think that calling up their citizens is very relevant at this point.
We're covered for foreign enemies. We aren't covered from domestic ones. Tell me, what good would your argument have done if terrorists had attacked again before the 2004 elections and President Bush had called off those elections and simply declared martial law coast-to-coast, then stated that he would remain as commander-in-chief until the threat of terrorism was over? Assuming the army stood with him, what's your plan B for year-10 of the George W. Bush presidency? For year 20? For year 30? Oh right, you don't have one. Just "let's all hope that doesn't happen (because I'd be screwed!)".
Same with the electoral college. In the good old days, the state would have a vote in November, and would select the person(s) that would get up on a horse and ride to Washington DC to represent the state in electing the president. There was simply no other way. The electoral college became obsolete with the telegraph, but it's still around.
No it isn't. Abolish the Electoral College and watch as "flyover country" becomes exactly that. The top 20 cities would get 95% of every candidate's attention and promises. Anyone living outside a metro area may as well not bother showing up on election day.
The stated reasons for the second amendment are no longer relevant, yet the amendment stays. Maybe the amendment should be updated to: "The right of the people to keep and bear Arms, for no reason whatsoever, shall not be infringed".
The amendment remains relevant because it - like most of the US Constitution - is less a practical guide and more a statement of principles. Principles like the government not dictating what religion we should follow or what opinions can be expressed. The Second Amendment is a statement of the principle that when all else fails, no matter what, responsibility for establishing and maintaining freedom ultimately falls on the people, and that as such, they must always have access to the tools necessary to fulfill that responsibility.
It doesn't matter whether the tyrant comes from halfway across the globe or from just down the street; the people - all of us - have the responsibility to ensure that no tyrant lords over us. The people having the convincing capability to beat any challenge to their freedom ensures no such challenge is made. Despite all the dire predictions of fringe leftists in this country, there was never a chance President Bush would crown himself king; if for no other reason than even he would have to know it would end very poorly for him. Tyrants don't come to our country because of the US military. Tyrants don't come from our country because of the Second Amendment. The idea that we don't need the Second Amendment because we have the military is as foolish as the idea that we don't need the First Amendment because we have the Internet. Modern inventions don't negate principles; they reinforce the need for them.