The service people of the mighty armies of the USA don't go round with tanks, fighter jets and all at their immediate disposal. Countries get notice of armed invasions. National forces take time to get mobilised.
A casual, pick-up militia has no place in the USA's military strategy. None. And this is why the 2A is an anachronism. When things get really tough the USA might invoke a draft and the soldiers get kitted out with army issue weapons. Not the guns they bring from home.
I repeat - not their personal weapons, and that's the truth.
Yes, it's totally and utterly outlandish. It aint gonna and can't happen.
But when armed US citizens (those militia-ready ones that 'carry', as you describe) show themselves capable of thwarting spree killings in US malls, cinemas and schools then I might begin to believe they could thwart an attack by armed-to-the-teeth and well trained enemy commandos.
You're describing a fantasy situation to justify a personal preference that is a result of historical accident. Accept that you have that preference by all means - and quote the constitution and the law if you like - but don't invoke fantasy situations to justify it.
See above. Firefighters and other first responders might need to go to their headquarters to collect their kit if they're not already on duty, and they get far less notice that they need to get about their work than those defending the USA ... THE friggin' mighty USA (seriously) ... from outside attack.
The US has no requirement for a militia in the 2A sense. None, zip, nada. The need to 'bear arms' in order to form a militia expired at the same time the possible need to form a militia expired.
But you're stuck with the consequences of the fact that that right is enshrined in The Constitution. Like I said earlier "You wouldn't want to start from here", but don't deceive yourself that you're not lost in the first place.