A few years ago, a policy change was made so that unregistered users could no longer post questions, only answers. The reasoning given by Jeff Atwood for not requiring registration across the board makes sense...
I found in my years of blogging at Coding Horror that the value of one person happening by with some gold nugget of absolutely the right information you need vastly outweighs the cost of ongoing moderation of anonymous posts.
...for sites like Stack Overflow, Super User, and Server Fault, as well as a couple others. It can absolutely happen that a random person can drop by, see a question they know the answer to, write it out real quick, and drop it on the question to the great benefit of the asker.
As a moderator of Christianity.SE...this doesn't happen. The community's standards have evolved since the early days so that answers are expected to be substantial and have support and references. The VAST majority of unregistered-user answers that I have seen have some combination of the following problems:
- not an answer (at all)
- not an answer (wrong scope/perspective)
- poorly written and/or formatted
- no support or references
- treating SE like a forum
It's bad enough that when I'm going through flags, if I see a user has 1 reputation, I look at their profile to see if they're unregistered. If they ARE unregistered, I am far more likely to just delete their answer (with a comment explaining why), especially if they haven't been around for more than a day, because I don't expect them to come back and fix the issues with their answer(s). If they are registered, I am much more reticent to take such actions.
In short, I understand Jeff Atwood's reasoning, and I acknowledge it works fine for technical sites. For a site like Christianity.SE, I honestly think that an unregistered user will practically never contribute a good answer. There's, well, pretty much no such thing as "absolutely the right information" on a site that is scholarly in nature. In theory, I do see that there could be such questions like "What work does this citation, <cryptic letters>, refer to?" that could in theory be answered perfectly by an unregistered user. However, in practice, such questions are extremely rare, and rarer still would be that a random person would just happen to know the answer.
My solution would be to enforce registration for questions and answers on some sites, like Christianity.SE. I honestly don't know how feasible this would be technically, and I understand if it's an unreasonable request. However, this issue has been bothering me for a few months now, and requiring registration would go a long way towards keeping average content quality high.
tl;dr: I believe that with some sites, the chance of some person happening by with a "gold nugget" of just the right information is practically zero, so there is a net detriment to allowing anonymous posts.