You're right, Hollywood hasn't helped things, but I also understand that the reason a hand grenade is dangerous is that the over pressure from the detonation of the propagating reaction of the chemical explosion causes a pressure vessel rupture physical explosion (See figure 2.1, Danial Crowl, Understanding Explosions, Center for Chemical Process Safety, 2003. - a book already open on my desk before this story posted to Slashdot). With a pencil case (the one in the video looked larger than I would have guessed) you're right that you'd probably have a non-directed overpressure wave, but ANFO would give a detonation shockfront rather than a deflagration one which leads to a much higher max overpressure to be translated to the surrounding air. Thus, even 10 MJ to 20 MJ in a small volume is still, if you'll excuse the pun, rather shocking.
P.S. Without knowing anything else, I would hazard a guess that your youthful experimentation did not meet optimum yield because you used a straight up agricultural conformation of ammonium nitrate rather than reprocessing it. Learning about that is much easier these days with Google rather than issues of Phrack or the (often inaccurate) Anarchist Cookbook from some BBS
A pencil box certainly has enough volume to cause a major hazard! An ammonium nitrate and fuel oil mix (easy homemade explosive) has something around 40 megajoules per liter energy density.
I think it's ridiculous what happened to the kid, and I'd love to see some public sense where it comes to electronics and chemistry (I believe it's illegal to privately own an Erlenmeyer flask in TX). That said, inaccurate claims about what can or cannot hurt people won't contribute to easing public fear (because they'll be debunked and then the reputation loss splashes further than the original reassurance). Instead, pick an argument which resonates with the region. For example, in Texas I'd point out that a failure to educate children about electronic or chemical safety is the same as failing to teach them gun safety. Guns are everywhere (in Texas), and children get hurt and killed when they don't know how to treat them safely. If that argument takes hold, then eventually enough people will learn enough basics about electronics and chemistry that this would have been laughed off before it went anywhere.
Telling people that something with the internal volume of a fewof hand grenades or a couple hundred 0.22 rounds can't hurt them isn't going to help.
I don't remember the word "personal" in the Second Amendment, but I do remember "That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it..." in the Declaration of Independence. That document claimed it as an intrinsic right of a people to throw off a government which no longer serves them.
I don't think a reasonable argument can be made against field artillery without at least addressing the Revolutionary War and whether or not it was justified or legal (i.e. via unalienable rights which trump lesser government laws against treason and rebellion). It is much harder to throw off a government without the ability to match its military capability. Regulation of arms (or militias) is a separate issue, but I think relegating the Second Amendment to only personal defense or hunting game without considering (modern) arms necessary to resist a depraved government's (modern) military would be an unwarranted assumption fallacy.
You get the 12 mile military and 200 mile fishing limits for your land per international law. However, this must be land above the water. You cannot find land under the surface, dump tons of dirt on it, and claim those rights, per same law.
This doesn't mean you can't create the islands, but you can't do the 12 mile/200 mile thing. China [a nuclear power with a massive army and permanent UN veto]
When all else fails, read the instructions.