Let me start by saying I don't approve of releasing classified information. Just so we're clear about that. Releasing classified info is a bad idea. People shouldn't do it, unless they're properly authorized to declassify and release it.
But here's the thing: when classified information is released, I'm pretty sure it ceases to be classified (recent objections to the contrary not withstanding). The definition of classified material is information that would cause harm if it were released. As soon as it's released (inadvertently or otherwise) the proverbial genie is out of the bottle and the damage has been done. The released information it can't be re-released any more than it can be un-released (particularly in this digital age), and once it's out, I don't think it can do any further damage by being "more out."
Because of that, I don't understand the recent ban on troops accessing WikiLeaks. Never mind the fact that we're saying the bad guys can look at this stuff but our guys can't, which has its own logical flaws. And it's not as if I really want to go read any of that stuff. I'm just confused because as far as I can tell, the released stuff doesn't qualify as classified anymore - unless I'm missing something. (And just to be clear: I have not personally visited the wikileaks site and have no plans to do so).
The other thing I wanted to point out was that we're talking about digital files. Asking that WikiLeaks return the digital documents sounds kinda funny to me - it's sort of like asking someone to return a fax by faxing it back to you. Yes, the Pentagon also asked that WikiLeaks also delete their files, but the request to "return" them made me laugh a little. Would they like the files to be delivered on a flash drive (which isn't allowed on government computers) or as an email attachment (which would get stripped by the file server because it's too large)? Maybe they could return the stuff by posting it on a website somewhere so the DoD could just retrieve the files... oh, never mind.
As for deleting, the doc's have already been posted online and copied by more than one or two people. So even if WikiLeaks decided to cooperate, that would simply mean they don't have a copy anymore... but it wouldn't exactly take the info out of circulation. Such a move might have merit as a symbolic gesture, but it wouldn't do anything (a-n-y-t-h-i-n-g) to solve the problem.
By all means, let's go after people who break the law. Let's encourage WikiLeaks (and others) to not solicit this sort of thing or repeat this sort of thing. If they've got a stack of unpublished classified stuff, let's encourage them not to expose it. But let's also keep in mind that we're not dealing with paper. Concepts like "return" and "delete" simply don't have the same meaning they used to.