Honestly, someone using Tor should know that your communication details are being held by exit nodes. Isn't it kind of common among the community to not trust your exit nodes?
I would say that the assumption is that your communication is public.
I would say that the assumption is that your communication is public.
The general assumption back when Silk Road was created was that TOR itself was safe, and the most likely way to be discovered was for your personal machine to be compromised. This belief was only strengthened by the FBI's repeated failures to take down Silk Road.
Heck, this was still a widespread belief AFTER Silk Road was taken down! For example http://motherboard.vice.com/read/the-fbis-deep-web-raid-seiz... quotes a security researcher who came to the conclusion in late 2014 that the FBI was just scanning TOR, and TOR itself had not been compromised.
For a comparison to phones, the Supreme Court has held that a list of people you called is not protected, but the contents of your phone calls are. Similarly I think they should rule in this case that the fact you're using TOR is not protected, but the details of what you were doing on TOR is covered by the 4th amendment.
What actually happened is the researchers found a way to bypass the middle guy and reconstruct the info just from the two ends. That's still just comparing notes, but from fewer people.
In our surveillance society, the government's theory is that it should never need a warrant, because terrorism. I strongly oppose that theory. I'm OK with taking down Silk Road, but get the warrant first.
Expectation of privacy is kind of based around self-incrimination, and you lose a lot of those when you hand information to a third party.
Even if it's "public" (in the legal sense of 'not protected'), Tor can be useful against non-state actors, or against weaker state actors.
I'm not saying there isn't a colloquial expectation of privacy, but that the jurisprudence on privacy doesn't apply to Tor (or at least, that there is an argument that it doesn't).
If government wants something forbidden, it creeps towards it. Expectations are meaningless without threats.