Update: I was involved in some very useful discussion in comments under @tinkeringbell's answer. It helped clarify some of the arguments against automatic deletion. If there's interest in this discussion, I recommend reading those comments.
I'll also note that this is not a feature request. As per the tags, I'd meant it specifically as only a discussion. Had anything concrete come out of the discussion, I might have then posed a particular feature for implementation.
I propose that all comments on non-meta sites be automatically removed after a certain amount of time.
It's well known that comments are ephemeral, and that if you think something is worthwhile in terms of addressing a question, it should be provided as an actual answer. Only answers are permanent. As such, there should be no expectation that comments won't be removed at any given time.
Having comments automatically deleted would enforce this message and also aid in site cleanup.
This is something that is constantly being brought up—the Why was my comment deleted? question. The response to that is always the same:
- It's not personal.
- Your comment was removed because it was part other comments that weren't serving a purpose.
- The comment was an answer in the form of a comment, not a comment that was helping to clarify the question.
Even for comments underneath answers, if the person leaving it objects to the answer or wants to enhance it, they can provide an alternate answer of their own (or, in the case of disagreement, simply downvote). If the person who provided the answer doesn't agree, the comment isn't going to make them change their mind if it remains for an extended period of time.
By making it explicitly clear that comments are ephemeral and not permanent, and then actually enforcing that automatically, it would help with the following:
- The complaints of comments being deleted in the first place.
If it's a stated fact that every comment will be deleted after a certain period of time, then complaints against those deleting them will be avoided. It becomes a function of the system, not of any particular moderator—whose deletions might or might not be consistent with those of other moderators.
- The appearance of favouritism on the part of moderators.
If everybody's comments are treated identically (over time), there can be no favouritism.
- The maintenance burden on moderators.
If comments are automatically deleted after a certain period of time, moderators don't need to worry about routine comment cleanup; they need only concern themselves with those particular comments of a uniquely negative nature that require immediate attention.
- The inappropriate nature of some comments.
If you know that your comment won't last long, it would force you to consider if you want to leave it at all, or if you should do something more appropriately permanent—such as leave an actual answer to a question.
A corollary to this is some kind of better notification that comments are ephemeral, perhaps by extending the add a comment text to add a X-day comment.
I am excluding the meta sites from this, since I know that comments in metas have a longer-lasting effect and purpose. However, even with the meta sites, it might make sense to include automatic deletion, albeit after a longer retention period.
I am also not mentioning a particular time period, because I'm not certain what would actually be appropriate. Some of the things that would be addressed by this would benefit from a shorter time period, while others would benefit from a longer time period.
The minimum period of time that comments are useful can vary depending on the frequency of the people checking questions and answers, as well as those engaged in a "comment discussion" that could lead to a worthwhile answer.
I don't think most people would say any comment serves a real purpose after a month, let alone a year. However, some serve no purpose at all at any time. So, some kind of sliding-scale-of-diminishing returns balance would need to be struck.
Is it reasonable to think that no comment serves a useful purpose—in terms of question or answer clarification—after 2 days? A week?