During the debate at Houston Community College, Professor Rakove a couple of times made the claim that the Second Amendment is obsolete because it is "about the militia" which is pretty well gone, and also claimed that firearms technology has advanced so much that what might have made sense then didn't make sense now. In particular, he claimed that one person with an assault weapon has as much firepower as a company of soldiers in the 18th century.
This didn't sound quite right, but I settled for pointing out that "assault printing presses" are capable of printing hundreds of thousands of pages an hour today--perhaps freedom of the press is obsolete. The Internet and modern telecommunications, perhaps, make traditional warrant requirements obsolete, too, by the same reasoning.
If I had been feeling really cheeky, I might have suggested that in the era of suicide bombers, that "cruel and unusual punishment" provision might not make sense anymore--that perhaps we need the ability to inflict suffering on convicted terrorists that keeps them alive, and in excruciating pain, for many years as a discouragement to terrorist acts.
But the more I thought about the claim about a single person having the firepower of a company, the more clearly wrong it was. With a 30 round magazine in say, an AR-15 or an AK-47, you can realistically expect to make 30 aimed shots in about 40 seconds. (Yes, you can fire all 30 shots in about 10-12 seconds, but they are going to go everywhere, and only in rather remarkable circumstances will most of those shots kill anyone.) That's about 45 shots per minutes, assuming that you can change magazines quickly.
A trained soldier in the 18th century was supposed to be capable of firing about three shots per minute with a musket. That means that a person with an AR-15 or AK-47 can put out about 15 times as many aimed shots per minute as an 18th century soldier. That's certainly a step up, but not equivalent to a company of soldiers--more like 1 1/2 squads of soldiers. It's an order of magnitude improvement.
Admittedly, the weapons have more range and are somewhat more accurate. (And I do mean that. Two minute of arc accuracy--getting all your bullets in a 2" circle at 100 yards--was relatively common for riflemen.) Compensating for that is the dramatically improved quality of medical care. Any abdominal wound back then was likely to be fatal because of peritonitis. The presence of city police forces who can respond to a criminal is an improvement over 1791, and the same improvements in technology that benefit a beserker with a gun also benefits those who are defending themselves.
By comparison, the "technological change renders this clause obsolete" argument can be applied like this:
1. A printing press putting out libelous statements about the government, or an individual, or obscene materials, in 1791 would have printed perhaps 4 pages per minute. A modern newspaper printing press prints thousands of pages per minute--so call it three orders of magnitude more potential damage.
2. Because of the limited size of American cities, the most that a newspaper of 1791 could have influenced with its partisan and dishonest reporting would have been about 10,000 people in a day (and usually much less). NBC News has tens of millions of viewers every evening; it is thus capable of spreading three orders of magnitude more lies than any American newspaper.
3. The most destructive individual weapon system of the 18th century was a warship, which could, conceivably, cause hundreds of deaths if it attacked a major port like New York City. The most destructive individual weapon system of today against which we have to defend ourselves as a society would be a nuclear weapon, which would likely cause at least a hundred thousand deaths from direct effects, and radiation aftereffects. This is at least three, and perhaps four orders of magnitude more severe of a threat to American society. By the same reasoning, if the technological advancements of firearms justify calling the Second Amendment obsolete, the protections against unreasonable search and seizure are far more obsolete. Oh, and for the same reason--to find out if such a weapon has been smuggled in--the 24 nightmare--not just waterboarding, but techniques that everyone recognizes as torture could be justified by Rakove's logic.
UPDATE: It occurs to me that the same is still true with handguns. I handled Paul Revere's pocket pistol some years ago. It was very compact--not much bigger than the Colt Mustang that I usually carry. True, it was only a single shot, while my Mustang holds six rounds. Still, people in 1791 America who were expecting trouble carried two, four, or even six pistols in their belt. (And there were multibarrel handguns at the time, known as pepperboxes, which were not as reliable as single shot pistols.)
My guess is that I could probably get about three times as many bullets on target in the same time with the Mustang as carrying six single shot pistols. Carrying a couple of spare magazines for the Mustang would take me up to about eight times as many bullets on target in the same length of time.
A high capacity 9mm handgun takes us up a bit higher--perhaps as much as 20 times as many bullets on target per period of time as single shot pistols. Still, this is an order of magnitude difference in capability--not multiple orders of magnitude.
Similarly, a modern handgun is more powerful than a single shot pistol of 1791--but until you get up to .357 Magnum, the difference in power isn't more than an order of magnitude. Accuracy is improved, especially because British-made pistols and many American-made pistols were smoothbores, but we aren't talking an order of magnitude. I would feel about as endangered by a 1791 single shot pistol at ten yards as I would by a modern handgun at twenty-five yards--a distance where a competent shot making a serious effort stands an excellent chance of hitting the target.