I've always read two trains of thought on the 2nd, but they both favor We The People. First was the founding fathers were generally afraid of standing armies, and their possible use by corrupted tyrannical governments to get people to toe the line. Since at that time the militia would be the day's "standing army," they thought the people should be armed with the same weapons, in case the militia was improperly used against them. The second train of thought, far simpler, was that the people themselves were the militia, and were expected to defend the homeland anytime it came under fire.
Personally, I believe the first TOT, since Article I, Section 8, Clause 16 of the Constitution grants the power to "regulate" the militia.
Could never understand the basis for an argument against it, that didn't simply favor elitism and a thirst for power.