Big deal. It is not as if it is something hard to DIY if you are committed to breaking the law. I think that is the stuff that both sides of second amendment shouting match fail to get - inventing deadly stuff is easy.
Would you have the same attitude about kiddie porn? What you say is true, but being able to buy guns from Tor will save you a lot of hassle over trying to manufacture your own. I think I am pretty open minded, but I was fairly shocked at what claimed to be available when I logged onto Tor to see what it was all about.
Logical fallacy: http://en.wikipedia.org/wiki/Think_of_the_children