Please god no, don’t turn Lemmy into 4chan

It's difficult to see how this could work without keeping the association between those posts and the person entity in the database. All it would take is one so-motivated instance admin to reveal the identity of the poster. It might still have value for low-stakes stuff, but it might give the end user the incorrect idea that their posts are truly anonymous.

Why doesn’t Lemmy implement this seemingly obvious feature?

It's so obvious I won't even mention it in the thread title

I imagine people are gonna abuse it for posting highly controversial takes that's borderline immoral if not illegal... People already do even with associated username, imagine if it's untraceable (by regular users) back to you. The nazis are gonna come out en masse, both who are trolling and actually serious. Seems like a moderation nightmare.

An option to mark an account as a burner when you create it could be interesting. Would allow for all kinds of unique functionality.

I think I see where you're coming from. You just want an occasional "incognito" option for posts.

If I wanted to help out another user and share the story of my struggle with genital warts, I'd probably be more comfortable doing that if it wasn't tied to my previous post history. Pour one out for Ken Bone.

My incognito posts would be subject to the same community standards as normal posts so if I used the feature to abuse or spam people, my real account would be affected.

I doubt there's so much of a technical hurdle here as an ethical one. It comes down to whether you feel you can trust your (unpaid, volunteer) instance admin to not spill the beans about your genital warts, and whether THEY are happy being custodians of potentially sensitive PII. The inconvenience of a throwaway is also its main advantage: it isolates whatever sensitive thing you want to share from both you and the admin.

Everything needs to be tied to a user at the protocol level. So the best way to implement this would be to generate a random username (GUID?), and set the display name to "Anonymous User".

But then you might as well let the users do that themselves, and the user can delete their account when they're done with it. Not that it would really harm to keep it around either way, just a couple wasted bytes in the database.

Metafilter had this back in the day. Exactly as you describe: just a checkmaek saying “post this as anonymous.” The admin would review and moderate these requests and if approved, move the post to an account named “anonymous” so that it was no longer even connected to the user at all. Then it would start showing up on the site. It was a good feature and met a real need. However I don’t think we need to be all “why hasn’t this happened already???” about it.

I think people would still create a throwaway to use once over using a feature that claims to make anonymous posts with your main account just to further distance any connections to the main account.

How does Reddit do it?

Maybe you would like Mainchan?

Might be able to set it up with an anonymous-reposter bot instead? Presumably this is for throwaway purposes more than confidentiality (the server owner will be able to track you either way) so having a bot (e.g. "@ThrowawayBot") that you could private message and have them repost might work.