so the people are the building blocks from which a society is built. everything in that society is a function of the people. so it is possible to assess a given society on a similar scale to the people: a certain society that has a certain distribution of certain kinds of people will experience certain outcomes. let us imagine that we take a large sample of societies and subject them to this idea where everyone gets their own personal nuclear weapon. in fact, lets boil it down to its logical core: let us imagine that every single person in society is given a button. if they press the button, the entire society will be instantly destroyed. they are all aware of this when they get their button.
on one extreme side of the scale or spectrum, a society filled with extremely smart, well educated, well adjusted and emotionally healthy people who all have great jobs and lives, in other words a properly structured society filled with very good people, not a single instance of button pressing would occur. you could in fact give each person the power to end the world and the world would go on unharmed. this is the goal. it can never be achieved because sometimes people go insane or have a bad break up or what have you, but its no different than an electronic device trying to use power as efficiently as possible: electronics strive for zero power consumption and societies should strive to reach the point where the aforementioned scenario is possible.
now we look at the real world. we see that gun control, voting, and all kinds of other things are actually the same thing: different ways in which citizens are trusted or not trusted with power. we see that in a healthy democracy or republic, the vote is far more powerful than the gun. we see that any healthy democracy or republic requires that its citizens are up to the task of handling power responsibly. and i think that if you agree with all the previous statements, you agree that much of the western world is in a lot of trouble right now. and say that without even the smallest shred of arrogance or snobbery.
so, this leads to a very interesting consideration of the limits of power that the citizens of the united states or the united kingdom might handle before something bad happened. and it is also fun to consider what the maximum amount of power the citizens are capable of handling after some kind of focused effort to make them ready. how much power could they handle if schools and jobs and everything were made better? what is the best outcome we might hope to achieve?
so the answer to your questions is that no, individuals probably shouldnt have nukes but they could probably handle some really dangerous stuff like chemical weapons or heavy machine guns if you just gave them the tools they need.
ExpectedHarm = P_incident * Harm
Weapons multiply harm, and education reduces P. Nuclear weapons cause ExpectedHarm to approach infinity almost regardless of P_incident, so they are out. But guns, knives, acid, and other weapons all sit along a continuum.
Increasing access to guns unquestionably increases ExpectedHarm (arguments like 'if everyone had guns, people would be well behaved' are, of course, ridiculous on their face), but there are social benefits to guns. Some people enjoy hunting, sport shooting, and carrying a gun makes many people 'feel' safer (which, though hard to quantify, remains a true social good, in some sense). Guns are also, to some degree, a check on government power. I don't particularly like the Bundy's position or what they stood for, but their access to guns is absolutely what gave them the power to make that stand. You can count this as a positive or negative depending on your perspective. I tend to count it as a positive even though most uses of it, like the Bundy's, I strongly disagree with.
And finally, there is the sort of 'constant' boost to the positive side you get from the general bias we ought to have against banning things (you may choose to set this to zero or negative if you hate freedom). So, the full equation is:
SocialGood + LibertarianBias - P_incident * Harm * BanEfficacy
If this expression is greater than zero, you should leave it alone. This does ignore some theoretical nonlinear terms (e.g. banning guns increases the probability of other forms of violence, or vice versa), but it more or less captures the idea. Depending on which values you input for various terms, you'll get a different answer.
All of that is to say that whether or not any given weapon ought to be legal should be evaluated according to a framework that looks something like the above.