TNT, along with other explosives, is a very useful substance, but it is also too dangerous in the hands of the untrained and unskilled to allow unlicensed personnel to have access to it. Nor are there any non-industrial uses for it that I can think of. Firearms are less dangerous and more useful for the general population and can be used effectively with far less training. They are also the weapons of choice when crimes are being committed, and homicide rates tend to be lower for societies in which they are less available.<quoted text>
If original intent is your criteria:
Dynamite is mainly used in the mining, quarrying, construction, and demolition industries, and it has had some historical usage in warfare. However the unstable nature of nitroglycerin, especially if subjected to freezing, has rendered it obsolete for military uses.
Since TNT was not invented to kill people, why is it against the law for me to buy it?
It all comes back to the basic tradeoff between security and personal freedom. I tend to lean more toward the latter, which is why I dislike many of the provisions of the so-called Patriot Act. I don't own any firearms, but I'm comfortable with the fact that many of my friends and acquaintances do and that some have carry permits. But it does make sense to clearly define where the line between the two is drawn.