Here's the thing.
Conspiracy to commit murder is pretty much 99.highNines% a "bad thing" and so if people do that, we have a good reason to drag them into court, and henceforth to prison. The fact that some assholes will do this is true; the fact that we want to then isolate them from everyone is also true. This, then, is a good law, because it does not interfere with everyone else's legitimate goings-on, and it can actually protect us from those assholes -- it's just about a perfect guarantee that if people are engaged in conspiracy to commit murder, it'd be much, much better for everyone else if they are stopped.
Carrying a gun is pretty much a 99.highNines% okay thing, as in, no one is going to get hurt by that, and so if people do that, we do not have a good reason to drag them into court, and henceforth to prison. The fact that very, very rarely, some assholes with bad intent will carry guns is not a good reason to tell everyone else they cannot carry guns. Further, as anything these assholes do that is actually asshole-ish already has a law against it (including conspiracy to commit murder, as above), we already have somewhat working tools to address, punish the actuality of, and in some cases even prevent, the problem. Do we need more tools? Yes, we do, because the problem continues to arise -- we have not solved it.
So, as to appropriate and effective tools: I think it's fair to say that most young who are in a state of mind of "I want to [kill|maim] [person|list]" have been pretty severely mistreated in one way or another. Classing, bullying, shaming, beatings and so on. Reducing that is where the effort should be applied by society. Not only because those things are bad, as they certainly are, but because they are known to be significantly contributing or primarily causal factors in this kind of acting out. Which, by the way, guns are not. The act of keeping and carrying arms is not what makes a person want to use it on other people. It's the wrong behavioral target. The problem is not arms. The problem is our defective culture, specifically in how our people, most definitely including our young people, treat each other due to perceived differences. Schools pretty much ignore this stuff. I remember all of it going on at a pretty good clip in my high school, and also in the high school my kids went to decades later. When they were bullied and shamed and I went in to talk about it with the powers that be at the school, I was told the kids "just have to work it out", which is, in my opinion, the root of the problem. No, the kids don't have to work it out on their own. The authorities should be eliminating the problem in every way possible, root, stem and branch. The entire competitive landscape in schools is wrongheaded, from academia to sports to any other means of holding up A as "better" than B. That's a whole different discussion, but that does provide a good overview of the problem.
Restricting arms won't solve the problem. Two reasons: One, it isn't the problem, and two, once someone is in the state of mind that says "I'm gonna [maim|kill] alla these fuckerz", they're already well past obeying laws, and well past caring about how it is done. So say there are magically no more guns. Does that clear the deck of easy ways to [maim|kill]? No, of course it doesn't. A little sword work, some mace swinging, a well-timed exercise of driving a vehicle into a crowd, home-made explosives, any number of poisoning mechanisms, sabotaging a bus, a well-set fire... it's just not that difficult to create huge amounts of mayhem, specifically or generally, by any number of easy means, even if all guns were magicked away. That is the core matter -- not how the mayhem is created. Guns are simply the preferred tool right now. Take them out of the equation, and it is a certainty that something else will become the preferred tool. Because all such a restriction does is take away that one tool. It doesn't take away either the motivation for mayhem, or clear the field of other tools that will work just as well.
Just as with the drug war, the problem isn't the substance / tool / implementation. It is the attitude that gets the person to the point where they care less about the follow-on consequences than they do about the immediate effects and the relevant act is perceived as an attractive choice. Also just like the drug war, the attack on the tool is wrongheaded, causes completely unnecessary harm to large segments of the population who will not be the source of follow-on consequences as they haven't been driven (or aren't naturally) batshit crazy enough to seriously misuse these things, and doesn't go any distance at all towards actually solving the problem.
Having said all that, I would further say this on guns themselves, in fact on arms of any kind: The constitution, as I read it, very clearly and without equivocation says we, the citizens, are empowered to keep and carry arms without government infringement. That would include, but certainly is not limited to, keeping and carrying guns. We are far better off changing that, if indeed we want to change it, using the constitution's article 5 mechanism, amendment, than we are tossing fiat law at the problem. Because if we (by which I mean the lawmakers, the lower courts, SCOTUS, etc.) can ignore one part of the constitution because we think it's old, or inconvenient, or (cough) is "living", then we can ignore the rest just as easily, and that means we're no longer a constitutional republic, in fact we're no better than any sorry-assed banana republic. Which, yes, I admit up front appears to be an exact description of our current circumstances.
I'm not even against changing our empowerment to keep and carry arms. If no arms is how the nation really wants to roll, then okay, then let's try that and see how it works out. I'll turn in my arms -- swords, guns, slingshots, whatever -- without protest if that becomes the legitimate law of the land (which is to say, there's an amendment to the constitution that says the 2nd is null and void or otherwise no longer clearly says that the government is not allowed to infringe on my right to keep and carry arms. Supporting laws that are clearly unconstitutional is an extremely bad idea, and almost all arms laws are presently unconstitutional when they infringe on the right to keep and carry, as they typically do.)
I'm just saying that (a) forbidding arms (either as infringing, unconstitutional fiat, or as amended, legitimate law) won't solve this particular problem as the act of keeping and/or carrying arms is not the actual problem, nor the cause of the problem, and (b) we're presently going about it in a way that corrupts the link between our constitution and our government, and that has almost uniformly resulted in bad things happening to the population at large, so we shouldn't be doing that.