I've encountered some Meta posts on the sites I am active or used to be active that complain about moderators' deleting comments without notifying the OP. Some OPs even complain that their comments are legitimate and should not have been deleted. Some raised the issue of moderators' abuse of power.
Most of the answers posted to the questions read:
Comments are ephemeral and they should not be treated as important as questions and answers.
OK. I got it. I would like to suggest the followings:
Comments with no upvote should be auto-deleted after six months from their posting.
Comments with less than three upvotes should be auto-deleted after longer-than six months but less than one year.
Comments with five upvotes or more should be auto-deleted after longer than one year, but less than two years.
However, moderators should not delete any comment unless they are flagged as offensive/rude/spam.
The periods suggested above are just based on my personal opinion. But I think this will help some sites, especially old ones with heavy traffic, clean up obsolete comments. Also, this feature can help users understand better why comments are ephemeral. They will not complain about it if they know the comments are actually and systematically ephemeral.
Your thoughts, please?