I see the Second Amendment as important, but not because of assault rifles, which I think it should be extremely difficult to get, especially given the epidemic of spree violence we've seen in the US. It's a historical note that is (sadly) still relevant today.

The Second Amendment is an admission by the federal government that it can't always protect people. This was an experimental federal government among states that didn't like each other very much, even then, in a world dominated by more powerful nations (like Great Britain, France, and Spain) and on an unexplored continent. (Taking a modern perspective, the Natives had more to fear from us than we from them, and they got screwed royally and are still being screwed today, but that's another matter.) The U.S. was so sparsely populated and rural back then, many people didn't have local police; the county constable might be a day's ride away. For a contrast: traditional European governments, at the time, promised unconditional protection but demanded unconditional subjection– before the Revolution, France was an absolute monarchy.

The Second Amendment was necessary because the upstart nation's government couldn't promise protection, given the country's vast size as well its vulnerability due to its small population. People needed to be able to protect themselves.

This raises two issues, though.

First, we live in a dramatically different world. We want the government to protect us when it can (and when we can trust it). Banning especially dangerous weapons, weapons whose main purpose is to kill large numbers of people quickly, is part of that protection. Most of us see it as a desirable trade to give up the "freedom" to own weapons we have no use for, if it makes mass shootings not happen. (This being said, guns are not the main reason we have an epidemic of mass shootings. Our economic system is deranged and, by design, produces extreme alienation and misanthropy.) It doesn't violate the Second Amendment, under most interpretations, for the US to make it difficult or impossible for people to stockpile assault rifles and high explosives.

Second, we no longer need the government to protect us from Native raids or foreign powers. Iraqis are not coming to our farms and absconding with our livestock. Rather, we need to be protected from, and– when official help fails to be able to protect ourselves from– corporate malefactors such as health insurers and purveyors of misinformation and our employers. That's not a fight that's fought with guns. Computer viruses, maybe. Hacking a health insurance company to reverse denials of care would be a heroic act and cause for jury nullification, for one example. The major 21st-century war (the global class war) isn't going to be fought mainly by people shooting at each other– it's going to be a war of information and against misinformation (further, against an economic system the people would not support except when inundated with said misinformation).