Volokh's blog has a discussion of the Second Amendment preserving the right to armed revolution. While I agree with what he says, and there is no doubt that the US Founders believed that armed revolution was sometimes necessary to protect their ideals, it just sounds kooky today.

Another way to look at it is in terms of the distribution of power. Some people want power to be more concentrated in (hopefully responsible) authorities, and others want it widely distributed. The purpose of the Second Amendment (in this regard, as I see it) is not so much to make armed revolution possible, but to make it unnecessary because the distributed power will limit what the authorities will dare do. It is analogous to the 6th Amendment right to a jury trial. The US Supreme Court has emphasized that this right stems in part from a desire to keep oppressive government power in check. Eg, it said this when upholding the right:

The guarantees of jury trial in the Federal and State Constitutions reflect a profound judgment about the way in which law should be enforced and justice administered. A right to jury trial is granted to criminal defendants in order to prevent oppression by the Government. [cites omitted] Those who wrote our constitutions knew from history and experience that it was necessary to protect against unfounded criminal charges brought to eliminate enemies and against judges too responsive to the voice of higher authority. [Duncan v. Louisiana, 1968]

Now rampant jury nullification is undesirable just as armed revolution is; the hope is that the decentralization of power makes it unnecessary by putting natural limits on government oppression.

Others don't see it that way, of course. The new International Criminal Court has no right to a jury trial.