This is undoubtedly going to be quite controversial and I'm braced to lose a fair amount of reputation but my stance is that allowing Tor users makes my life as a moderator harder and I don't think that's a cost we need to bear. If you're a Tor user, I'd like to hear why you're a Tor user (I'm not so I might not understand) and by extension why you think this is a dreadful idea :)
Here's my argument for blocking Tor users from doing things on the sites:
- Tor makes it ridiculously simple to abuse Stack Exchange. Sock-puppets, voting rings, spam and harassment, we've see all of this come over Tor where Tor was required to stop the automatic alarm bells going off.
- Not all Tor users are evil, cheating trolls but do legitimate users need Tor for SE? We're not hosting porn or manuals on how to overthrow the communist state (none of the sites is blocked in China, it seems), so is there a reason we should be aiding people to connect via an anonymous proxy service?
- By extension, I have zero sympathy for people using Tor to get around local network blocks. You shouldn't because circumventing network security is usually an actionable offence (and they'll catch you if you're using Tor).
- Local privacy (sniffing et al) isn't so much an issue any more since SSL was enabled everywhere.
- This is trivial to enable. Keep a local list of all the Tor nodes and check when the user does something. By that I mean POST but you could move that to specific actions.
I know that blocking Tor wouldn't solve all our problems but it stops the laziest. It forces would-be spammers to rent a botnet or use another less-stable or more illegal or more costly routes into the sites. In short, none but the most determined are going to bother us and even those will run out of steam sooner than the others.
And they'd still have readonly access if GETs were allowed through.
I'm surprised that no SE moderators have brought this up before. Perhaps I'm just famously bad at searching for things or it's been proposed and stoned to death multiple times...