<IANAL> His trial probably wouldn't be a proper venue for that. Those principles are that the laws he's accused of breaking shouldn't exist. This would be a very difficult defense to make in a criminal court, which both presupposes the credibility of the laws on the books and its own legitimate capacity to adjudicate them.

The court of popular opinion seems to be edging ever so slightly in Ulbricht's favor. Morally and politically, arguments for minimal government and drug legalization might have some merit. But no one is ever going to convince a judge that, while, the defendant might be guilty, the real crime is that there are even laws against everything he's accused of.

Although I suppose he could use the opportunity to make a statement anyway, regardless of how well it works as a legal defense. I wouldn't blame him either way, really. </IANAL>