Peter Frase offers a good view on how 3d printing may acquire a scary reputation. It might start with gun printing.
[G]uns, and other dangerous objects, will surely be used as the pretext for a much wider crackdown on the free circulation of designs and 3-D printing technology.
Compare with copyright:
When the copyright cartels were still only trying to control the circulation of immaterial goods like music and software, they faced the problem that it was hard to convince people that file sharing was really hurting anyone. Notwithstanding a few lame attempts to link piracy to terrorism, the best they could do was point to the potential loss of income for some artists, and the possibility that there would be less creative work at some point in the future. These same arguments will no doubt be rolled out again, but they will be much more powerful when linked to fearmongering about DIY-printed machine guns and anthrax.
Watch for it.