I think it must be that simple. He can't be working for us because he's put a lot of people in danger:
In the end, all the efforts at confidentiality came to naught. Everyone who knows a bit about computers can now have a look into the 250,000 US diplomatic dispatches that WikiLeaks made available to select news outlets late last year. All of them. What's more, they are the unedited, unredacted versions complete with the names of US diplomats' informants -- sensitive names from Iran, China, Afghanistan, the Arab world and elsewhere.
Sadly, WikiLeaks has less disciplined rules of engagement. I'm sure they'll find that the resulting deaths and arrests are acceptable collateral damage.
But since he is at war with us using a private entity as his weapon, why can't we treat him as a combatant?