Re: Trouble is
"perhaps I could interest you with the mathematics of designing H-bomb warheads that can fit into a MIRV....."
It's been 50 years. Do you honestly think that The Register's readers couldn't build a relevant miniaturized implosion core if we wanted to? I personally don't know the math off the top of my head, but I know enough to know what questions to ask and where to find the answers. The rest is learning and simulating. That can be done on Amazon these days.
No, civilians - and for that matter most nations - don't have nukes because they simply have no use for nukes. Nukes are great for establishing you as a sovereign power, but they suffer from three fatal flaws.
1) They're outrageously expensive.
2) They're absolutely useless unless you have multiple launch systems that can participate in MAD.
3) Unless you have the conventional resources of a nation-state you can't defend them against the current signatory powers of the nuclear non-proliferation treaty who will take your toys away from you.
Even a "terrorist" has no use for a nuke. Let's say some crazy ISIS Jihadi blows up New York. They don't gain anything by this. They don't fracture the USA, sow terror or otherwise do anything but kill a few infidels. What they absolutely will do is cause the entire rest of the world to unite against Islam, get the entire middle east turned into a sheet of glass in retaliation and trigger an anti-religious genocide the likes of which this world has never seen.
They know it. We know it.
Even if you were completely batshit crazy and wanted to wipe out a city or two...you don't need a a MIRV to do that. You can pack relevant "kaboom" onto trucks or boats and get things into the city in far more mundane ways.
If you're really smart you wouldn't even use a nuke; every major city in the world has radiometric sensors so good luck with a nuke. If you want an earth-shattering kaboom go with fuel air bombs. Pretty much untracable, and from they pack the punch of a small nuke. (Especially since you need to detonate the nuke somewhere around 1700 ft in order to actually make use of the plasma shockwave.)
Of course, MOABs are flash-and-gone. If you had access to fissionable material - which to make your fusion MIRVs you'd need - then why not just build a dirty bomb? If you're truly nuts and want to kill a lot of people in a horrible fashion that's pretty much the worst possible way. Or you could poison water supplies. Or...
*shrug* I could do this all day. The last time I played this game I think I hit 83 different designs before I ran out of ideas. My point is this: the overwhelming majority of people, including "terrorists" have no use or desire for weapons of mass destruction. Unless you are already a powerful nation-state, they don't offer the individual or the organization any value, and cost them rather a lot.
There are always crazies, like those wackos that murdered cops in Nevada a few weeks back, or folks like McVeigh. It is for this reason that we control access to the kinds of materials necessary to make the really neat toys. That's part of the "eternal vigilance" price of freedom.
But you can't control knowledge. The genie, once out of the bottle, doesn't go back in. There are literally millions of people on this planet that could build you a basic gun-type fission bomb from memory. Hundreds of thousands that could design you a fusion bomb with a little effort. Any wacko at any time can kidnap and torture these people until they give up the how.
But he can't do a damned thing unless he can get the fissionable material. Or a metric tonne of Strychnine. Or...
People who have the resources to get WMDs have thus far been reluctant to actually use them. That limits the terrorists to small-scale attacks that at best wipe out a few city blocks or a subway station.
If you want to fret about something, freak out about the concept of "designer DNA". This is a thing that you can do, if you have the right equipment. The skillset and knowledge are about where nuclear weapons were in the late 50s.
Give it 60 years, and there will be millions of individuals capable of designing "printing" DNA, then injecting it into a bacterial host of their choice. How do you control that? The raw resources required to do this are impossible restrict and the fundamental knowledge is already in the public domain. All that is required is commoditisation of the technology, something that is already being worked on.
The true "threat" to our individual and national security is not going to come from the sharing of government secrets, because the technologies the government developed were developed under the watchful eye of true paranoids. They worked out how to control those kinds of technologies long before we proles ever heard of them.
The "threat" techs are those coming out of the commercial and academic sectors, where they go through layers of peer review and even commercialization before the paranoids ever get involved and go "hey, wait, this could go really badly."
A terrorist with a nuke will only get himself and his entire religion wiped off the face of the Earth. A lone nutjob isn't going to get the material to ever build one...but both of them could be building designer plagues within the next 50 years and we'd not only be unable to figure out who unleashed them, we might not be able to contain them.