This current legal challenge is in regards to a two year old letter from the U.S. State Department stating that Defense Distributed was violating U.S. law by posting a file to the internet that was the blueprint for 3-D printing a pistol.
The legal argument is that the file is free speech and is protected by the First Amendment.
My personal opinion is that with CNC machines and 3-D printers dropping in cost, any attempts to regulate what can be built will simply be in vain. The internet empowers the entire world with knowledge, and the ability for a people to make their own weapons could possibly lead to revolutions in countries with dictatorships.
America rose up to fight against the Brits using firearms, and we won our freedom. What if North Koreans were able to print their own guns to stand and fight against Kim Jong Un? Or Mexicans who need to protect themselves from corrupt cops participating in the drug trade? You know, that whole tyranny thing.
The internet paired with 3-D printers and portable CNC machines could be a liberating force for good.
The above is my opinion, but for more, Wired covers the story more in depth: