It was specifically because the people wanted the right to defend themselves; they specifically did NOT want to be disarmed by the new government - they did not want to be like the bulk of european nations - whose governments could not trust an armed populace not to revolt. We were supposed to be a government of the people.
Then, like now, the people did not want to give up thier guns to any government.
The militias of the time fought BEFORE there was an army; they were groups of unpaid citizens. THAT was the definition they used - or do you think they changed the definition of militia that they used at the time specifically for the Bill?
As far as individal States definitions go, States had FAR more power, then - the Bill was intended to trump any State law. Once again, it is not the 'Militia' part of the amendment which should be looked at, but the "well regulated" part. Well regulated militias would provide training with the weapons, some discipline, and also preclude your "bunch of kooks" argument.
Even if one were to accept your arguments, we would STILL have the right to keep guns after we left the armed forces, for at least as long as we could be called to serve again.
THe whole point of the Bill was CITIZENS rights, not government privelege, no matter what gun control nuts say.