I have no idea what you think of as “defensive purposes” then, because I could definitely threaten an aggressor to launch my nuke at him if he tried to hurt me. As a side note, I don’t think anyone in a free society would ever own a nuclear weapon. Individuals can get their hands on them today if they wanted to, but guess what, they don’t.
Where does the funding come from to build nuclear weapons? If it were a stateless-society, who would invest money into the production of a nuclear weapon? It obviously wouldn’t be the average citizen. Would it be economical for an individual or more likely a company to obtain a nuclear weapon for whatever benefit? Even though they exist, an individual obtaining a nuclear weapon seems highly unlikely. If anything some sort of group would have to obtain it.
The folk with the best nuclear weapons policy on earth are the brits: they keep the minimal number of SSBNs to maintain at all times a 24/7 nuclear force on the sea with 300 nukes, just enough to destroy every county on earth which might attack. As far as I’m concerned the brits could very easily disband the whole army and kekp only those 4 subs. So, every move towards a more ‘british’ policy is good. Obama’s treaty is good, as the US has far, far too many nukes, but unilateral disarmament down the british level (but not below, as only folk which want a new total war can possibly want) would have been preferable. Here state interest coincides with the general interest. As for ‘crazy people’ getting nuke, I look very hopefully forward to the day when nukes shall cost a million bucks apiece, as that alone would practically end all military conflict on earth and the world would revert back to thousands of microstates. A blessing for humankind. So let us hope that Iran actually produces nukes setting of a nuclear armament race in the region, and possibly further. Here state interest is clearly agianst the general interest.
If it is opinion that the only plausible reason for owning a nuclear bomb is criminal, it is opinion that a man lunging at your throat with a knife has only one plausible intent: criminal. You could suppose, if it suits your interest, that he is just practicing and will stop just before he reaches your throat. I prefer common sense when dealing with my own safety. Right and wrong may be theoretically clear cut. However, theory does not judge real situations.