Background

The Stewards are the only community-elected group of users that has the centralauth-unmerge user right. This allows them to delete global accounts and/or unmerge local accounts from the global account (in other words: detach an English Wikipedia account from its global counterpart).

Global account deletion is virtually never necessary. Despite what it might look like, global account deletion does NOT remove all traces of the account from the system. Instead, it removes the global account _itself_, leaving all the individual local wiki accounts dormant. As of now, a global account is required for logins to be possible, so deleting the global account removes the person's ability to use Wikimedia. When global accounts were being introduced, global account deletion was used to "opt out" someone from having a global account. However, this use-case no longer exist.

It is worth noting Steward-level access is not sufficient to reverse an accidental deletion. For this, a sysadmin needs to intervene. A recent example of an accidental deletion that needed reversal was logged as T396091: Fix accidentally unmerged global account.

Account deletion is -- very rarely -- necessary to resolve certain technical issues (for example, when a new wiki is attached, and duplicate accounts are mistakenly created). However, when that happens, sysadmin-level access is usually needed (if you want to change how accounts are attached, or resolve duplicates), as Stewards cannot merge global accounts by themselves. Even if a Steward finds themselves in a need of an account deletion, they can easily (and temporarily!) assign this permission to themselves, do what they need and then remove it again. Not having the permission by default will greatly reduce the possibility of accidental mistakes, as demonstrated by eg. T396091.

Suggestion

Remove centralauth-unmerge permission from the steward group.

Notes

Logs demonstrating the uses of the feature