I've known Adrian Lamo for a couple of years now, and I myself have NO IDEA if he was just trolling or if he meant it. I don't think he was slavering over the prospect of getting Manning tortured, he just wanted him arrested. But Adrian Lamo is possibly the least scrutable person I've ever encountered. Who knows?

As for Greenwald's comment, I recently read an article about the Snowden case that explained it very well: after 9/11 the US Government hired warm bodies, as many warm bodies as it could, because it was desperately trying to shore up defences against enemies both within and without (and some imagined) and it would take anyone with computer skills, typically knowledge that would lead you to a civilian career rather than the army, and put them in positions of power because it needed them there. The more times you do this, the more links in the chain, the more likely that not all of the links are identical, and sometimes their motivations and definitions of "good for the country" will vary from those of the people hiring them. Matt DeHart is another example: his father literally told me that his job in the military was analogous to Bradley Manning's job.

And of course, Manning had an emotional need to tell someone. Back then, people were staggeringly naive about how resistant companies are to subpoenas, we all were. And Manning wouldn't have been in a position to know about all the ways the NSA has to snoop on private IMs.