Is not having contact information
Consider if you will, the unfortunate user discussed in this MetaFilter metatalk thread:
His post wasn't really that inflammatory, but I think the level of trust is really low for people who can't be contacted offline. Total anonymity and community membership just may not mesh very well.
Many MUCKs require email authentication (you sign up in "person" on the muck or by the web, and your password is emailed to you), and some don't take Hotmail, Yahoo!, or other common free email services. A common reason is to (mostly) uniquely identify someone as one person, so if he misbehaves enough to be banished, he can be removed with more accuracy.
Some very small, very new MUCKs also say this, and it seems brandished as a badge of authenticity: we're concerned about your accountability, therefore we're a safe, good place to play. That or it just sounds mature.
Giving out some bit of personal information is the cost of entry to a lot of online places. I give my email address, therefore I'm accountable for my actions. If I make one up, or use an anonymous one, I can't be held as accountable.
On the other hand, I've read a couple good anonymous posts on Half-Empty of late--the best system for a news/community site seems to be only authenticated account-holders being able to post, but having the option to post anonymously. Players on all MUCKs I can think of are promised in system policies that their identities won't be given out arbitrarily. Requiring a valid email but allowing "anonymous" ones like Hotmail or Yahoo! seems popular in the MetaFilter thread.
At any rate, personal identification with something as simple as requiring a valid email address and with what limits is important for Internet discourse.
