Unless I missed something, they don't touch legality of Tor, other than: "Further, we believe that running a Tor relay — including an exit relay that allows people to anonymously send and receive traffic — is lawful under U.S. law."
This doesn't say anything. I can "believe" anything that I want, but it doesn't make it so. I'm looking for articles with sound legal rationale and previous case outcomes that argue on the legality of a defendant's culpability as it pertains to a crime being committed on said defendant's Tor exit node.
No-one has ever been prosecuted for running a Tor node in the U.S., so the information you're looking for simply doesn't exist.
That's why we have to go on the beliefs of lawyers familiar with the area, instead. You could read about things like the Safe Harbor provisions of the DMCA to see why Internet service providers are generally not considered responsible for their users' actions, in the U.S.
The DMCA safe harbor (OCILLA)[1] protects against copyright issues. I don't have time to find the laws that apply more broadly. Any laws that protect service providers are going to apply. Tor is just a proxy.
I don't know why you'd think it wouldn't be protected just like an ISP from users who view kiddie porn or FedEx for shipping drugs. So long as you cooperate when the law comes knocking you should be fine.
