...and take from that there should be no regulation on bearing arms? Or that people not part of a formal (i.e. well-regulated) militia should have any right to bear arms at all?

Because the amendment specifically says that it is the militias, not the people, that are regulated.

Why not just formalize militias, give them the right to bear arms and restrict the storing of those arms to a militia armory?

Because our government was formed as a series of checks and balances. From our branches of government, to a decentralized military, to the people who made up the decentralized military keeping and bearing their own military arms.

If you disarm the people, and give over the arms to the militia, then he who controls the militia armory controls the militias and thus the people.

The problem that I am coming to have to see and admit is that the entire premise of the system, as I said before, is checks and balances. The founders felt that it was a good balance for the people to be armed. This worked in their day because in order for the people to be a threat to any oppression they would have to band together - into a militia - to counter that threat. As an individual, an armed man could not on his own effect any policy change through force of arms, nor be of much harm to his neighbor. Yes, there were armed rogues who raped and robbed and murdered but, generally speaking, no one armed man could hold many men at bay for very long.

Today, what we have seen is that the balance is destroyed. One man now literally held a life-or-death sway over 20,000 people. That is one-quarter of the size of the entire Continental Army.