I recommend that SE give individual sites the option of permanently barring unregistered guest accounts from posting answers.
Granted there is a long-standing policy of allowing guests to post answers without account logins, for example, as shown in the answers here (all between 5 and 10 years ago):
- Why doesn't Stack Overflow require registration?
- Encouraging users to create an account (and keep it)
- “Post as guest” is a bad user experience and encourages low quality contributions. Get rid of it
- Can unregistered users be blocked from answering on some sites?
By way of justifying the re-request for this feature, note the following: The kernel of each of the answers above (saying in each case that guest answering ability would be retained) come from the SE founder Jeff Atwood in 2011 (9 years ago as I write this). Since that time, the SE network has expanded significantly. In 2011 SE started with only 33 sites; Jeff left one year later; now SE has 176 non-meta sites as of this writing (an over 400% increase). The blog in 2016 specifically noted that the network was adding sites that, "push the boundaries of traditional Q&A".
The essence of Jeff's mark on the issue, in 2011, was this (emphasis his):
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.
My observation is that this stance is entirely focused on the issue of technical coding problems, in the question-and-answer format, such as seen on Stack Overflow or Jeff's older Coding Horror blog. In these cases there is quite likely to be a relatively clear-cut, narrowly technical solution to a specific problem that may help the original poster of the question.
But this is much less likely to be the case for many or most of the other sites that SE has added, since Jeff left, many of which are self-admittedly not in the traditional Q&A mold. Many other sites tend to deal with much more subjective areas, which may have a wide range of philosophical opinions toward them, and are more likely to attract the interest of ideologues who feel motivated to regularly push their opinions into a variety of otherwise unrelated questions, lowering the quality of the site as a whole.
Case study -- On one of the SE sites I frequent, there is a long-time guest poster who remains without a registered account. They post an answer to almost every question asked on the site, putting forward the same counterproductive position to everything asked there, regardless of topic. In addition, their posts and comments are usually rude and/or dismissive of other posters. They are almost always downvoted to the bottom of the list, but: (1) this takes time and energy from other people on the forum, (2) points are spent by readers of the site on the downvotes, (3) the fact that this poster always posts as "guest" means that they can recycle the account back up to zero reputation at any time, (4) new posters cannot identify or see past history of this user, (5) moderators are stumped at how to contact/communicate with them, and (6) they are not subject to any possible ban.
This situation has been an ongoing problem at Math Educators SE without resolution for at least the last 3 years. A similar recurrent case has been happening at Music SE for at least a year and a half now. I see comments that Sound Design SE and Photography SE also have the same experience.
In short: By remaining a perpetual "guest", a visitor can effectively spam every question on a site with some ideologically-inspired viewpoint, and avoid all of the normal moderation and tracking mechanisms. While this would be hard to imagine on a purely technical site like Stack Overflow, in 2020 it's a daily occurrence on the wider array of more subjective Stack Exchange sites.
I'll also recommend that you read this question from 5 years ago, where a moderator of one of the SE religious forums provides different but complementary reasons for the same idea -- but which SE Community Management, in comments, seems to consider distinct, because it doesn't explicitly ask for moderator-controlled decision-making, or use the word "permanent" in the feature request.
So I'll argue that Jeff Atwood's original position may have been useful for the initial Stack Overflow and closely related technical Q&A sites, but no longer holds for the majority of sites on Stack Exchange. Please give other sites the option of prohibiting unregistered guests posting answers, on a permanent basis, to be used at the judgement of members of each individual site.
Note: Previously this question was marked as a duplicate of one of the links above (Can unregistered users be blocked from answering on some sites?). However, in comments there, the SE Community Manager (Catija) drew a distinction between what I'm asking here and the one there:
I think you're confusing your request with the one here... this request does not in any way ask that a moderator be able to turn it on and off... it only asks that it be possible to have it blocked - and it is possible, we [the company] just almost never do it.
Another staff member (Tim Post) further emphasized that SE has never to date considered turning off guest answers for any site on a permanent basis:
I've been involved in abuse mitigation for the last 6 years and we only flip that setting on in extreme cases where someone (or something) is flooding a site with spam, harassment or gibberish. We've yet to encounter circumstances that would cause us to consider a scenario where the setting would be enabled permanently.
Again, I'm asking that moderators of individual sites get full authority to turn off guest answers on a permanent basis. If I'm reading the SE Community Manager's comment correctly, then this question is not a duplicate of the linked question (at least in the eyes of SE network administration). This question was therefore re-opened on that basis.