We don't actually know for sure that he was doing "illegal things". He was running a hosting company ("Ultra Host") on the public facing web and later launched Freedom Host as a side business, or perhaps better described as a charitable hosting service to contribute to the Tor network. Freedom Host offered FREE hosting to people on the Tor network. What liability does he have if other people use his host for illegal things? From what I understand he was never personally involved in any of these activities.
One can argue that he had to know about it, perhaps so, but the way he's being portrayed by LE and media is as if he was the kingpin of child porn. That's far from the truth. Freedom host served half of the Tor network, including perfectly legitimate services like Tormail, wikis etc.
I think his mistake in not cloaking the identity used to purchase servers can be explained this way: He was never planning to host CP starting out (or do anything else illegal for that matter). He probably thought universally recognized no-liability laws would apply to Freedom Host just as any other hosting business. Perhaps he later went down a darker path, but at that point it was too late.
The fact that he now pleads guilty means absolutely nothing however. Remember, he was extradited from his country to USA, and while he should never have been sent there, he now have to adapt to the way the "justice system" works over there and it works kind of like this: 5000 years in jail or take a plea deal and get away with 15-30 years. Even if he is innocent, you need to realize that when you're facing a kangaroo court and subsequent rotting away in jail for life it might be better to pick the lesser evil.