Made all the more problematic by the question of whose purpose should be used. It's a piece of open source software with multiple contributors, one of which may or may not be the node operator. So whose purpose do we use? The US Navy? The EFF? The node operator? They may each have a different purpose.
> And actually, purpose requirements in law are not uncommon and, in systems with meaningful proof requirements that benefit they accused, since they provide additional facts which must be established by evidence before punishment can be imposed.
Purpose requirements are typically sentence intensifiers for things that are already illegal. Illegal entry is trespass but illegal entry with intent to commit a separate crime is burglary.
The problem here is that the other requirements are completely normal behavior and it's the purpose requirement which is doing all the work. If you take it away you don't have a sensible prohibition on something wrong which the purpose requirement only makes harder to prove, you have a nonsense law that prohibits ordinary upstanding behavior. In other words, without the purpose requirement there would not sensibly be any law against this to begin with, and that is what would really benefit the accused.
Says who? According to the torproject.org homepage[1], the purpose is:
> [to help] you defend against traffic analysis, a form of network surveillance that threatens personal freedom and privacy, confidential business activities and relationships, and state security.
That includes stuff like preventing your ISP from knowing private personal details like how one was fired, or is secretly gay, or likes to write or draw porn, etc.
Also, if you own a big business and you just bought a supplier to eliminate the costs of a middle-man, you might also want to keep that confidential from your competitors for whatever business strategy you have.
The US Naval Research Lab that developed onion routing, patented it, implemented it in the form of Tor, and released it under a free license, which is how the outside-of-government (though founded by some of the same people who had developed the tech and implementation at the USNRL) Tor project was able to build on it.
Edit: On further reading the distinction is the TECH behind tor was created for that purpose, TOR itself was created for what it says on the tin.
While it's possible that Tor's stated mission was a smokescreen, I think it's much more probable that it as created just as its creators said, as part of information assurance (i.e. allow dissidents and journalists to get information out of repressive regimes).
https://www.onion-router.net/Sponsors.html
...states the early generations were created by Navy R&D. The purpose was protecting U.S. government assets with widespread use providing a smokescreen for them, letting them get lost in the crowd. It also took funding from Navy CHACS, which does high-assurance security. The CIA also wanted to protect foreign dissidents in their efforts to change regimes. So, it was getting funding from State Department or a CIA front last time I checked that works on stuff like that. Majority of its funding. It would probably go into legacy mode with layoffs if U.S. military and intelligence stopped using it. They'd have no need to pay the developers' salaries.
So, anyone telling you it was designed for something other than supporting U.S. military and intelligence operations is either ignorant of its history or lying to you. That said, it did evolve to help all kinds of people who have nothing to do with such operations. I always give out the "Who Uses Tor?" page for people wondering about legitimate uses for online anonymity. It's an awesome page.
https://www.torproject.org/about/torusers.html.en
EDIT to add CHACS Accomplishments since they brag on what they achieved with Tor:
Similar to the Internet.
Even so, that's just as much facilitating illegal (under local law) activities as protecting US overseas intelligence activity is, and actually overlaps substantially with protecting US overseas intelligence activity. (US intelligence assets often being dissidents, if not always overtly so.)
? It's also used by journalists in countries where browsing for certain kind of information can get you in trouble. Intent is what matters here.
While that's perhaps an interesting question in the general case, for Tor, we know the purpose was to protect US covert intelligence communications overseas, which is very much about enabling illegal (by local law) activity.
And actually, purpose requirements in law are not uncommon and, in systems with meaningful proof requirements that benefit they accused, since they provide additional facts which must be established by evidence before punishment can be imposed.