One of the amendments would have stopped people on the FBI's terrorism watch list from purchasing firearms, which opponents thought would be terribly unfair for the occasional person who winds up on the list improperly. That's a common refrain--what about the law-abiding person whose liberty to buy and use guns gets infringed by efforts to disarm the next mass killer? If you close loopholes, making it harder to buy guns at gun shows and online, what about the law-abiding gun enthusiast?
I suspect liberals and conservatives are as far apart as they are on gun control partly because of the way they feel about this figure--the law-abiding gun enthusiast. If you think gun possession is important, meaningful, and worthy of the highest protection, you won't want to see anyone inadvertently denied gun liberties, as a result of being mistakenly put on a terrorism watch list. But why see it that way? Why not see a gun owner as being like someone who wants to own a tiger or drive at 100 mph? What makes gun ownership special?
Self-defense. The problem with thinking gun liberties are special, based on the role of guns in self defense is...what role? If you give a population access to guns for purposes of self-defense, a few will use them that way, but far more will wind up using the guns non-defensively--there will be accidents, suicides, domestic violence that turns deadly, and yes, murders and mass shootings. Having a gun is crucial for sustaining a certain type of fantasy of self-defense, but not for keeping yourself and your loved ones alive. So we really can't say gun liberties are special and deserving of the highest protection because of the role that guns play in self-defense. (Analogy: having a tiger for self-defense. It might work occasionally, but policy-makers would be right to ask how often it works, and at what cost in tiger-caused deaths and maulings.)
The second amendment. Another allegedly special element of gun ownership, in an American context, is the second amendment to the constitution. "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed." In a modern context, a "well regulated Militia" would have to have the armaments of a modern state--bombs and tanks and the like. Nobody really takes the second amendment seriously as carving out specific liberties people ought to have in the 21st century. We can limit people's access to bombs and tanks, stopping them from forming effective militias; so what relevance can the militia standard really have?
Hunting. If you don't have a gun, you can't engage in recreational animal-killing. This can't be taken seriously as a reason to specially protect gun liberties, more than other liberties we might like to have. If it's valuable at all to be free to kill animals for fun, it can't be so profoundly valuable that gun-ownership is entitled to special protection.
Gun play. Finally, there's the liberty to spend leisure time hoarding the biggest guns available and acting out fantasies that are encouraged by endless video games and movies. This is a reality for thousands--maybe millions--of Americans. And I do buy that more liberty is preferable to less, even when it comes to activities I personally find repulsive. The question is whether this sort of pastime is worthy of heightened protection, more protection than we would award to activities like driving fast and harboring tigers. But no--how could it be? Gun play may be wildly fun for some people, but fun is just fun.
There is really just no good reason to protect the liberty to have guns more than we protect the liberty to drive fast or own a tiger. Gun liberties are not at all like liberties in the sphere of religion, speech, conscience, and political participation. I would be worried about abridging those liberties for everyone on the FBI's terrorism watch list--worried on behalf of people who shouldn't be on the list and even on behalf of those who should. But those are entirely different dimensions of life.
When we're discussing gun liberties and rights, we should remember that guns are just guns. There's nothing sacrosanct about having and using guns. How could there be? The gun crowd has won half the battle when they make us attach some special value to gun possession, as if it were particularly profound and vital to life. No--having guns is just one liberty among many others, abridegeable not without reason, but when necessary for public safety.