Lack of enforcement is not a good argument here, especially since it is very hard to prove that a citizen without a security clearance knew information was classified.
I'm not arguing for no enforcement. Leaving government employees out since that's covered under different legislation, proving possession is easy, if the media, or anyone else, discloses classified information, that's a defacto admission. My guess, if these cases were actually prosecuted, the result would be a shifting of the burden of proof to the accused.
If this case proceeds, the amicus briefs will be voluminus, every media and lobbying group in the country will have their 2 cents.
If we're going to prosecute this, and I don't think that's necessarily a bad thing, we probably need new legislation.