While I do realize that it's chatter and isn't that important in the grand scheme of things, it is still a public sanction, and public sanctions of all sorts should have public notice made of them, as well as some means of tracking them over time. For things like being borged, a simple note of the user in the belly node is sufficient along with notice to the user in question. For deleted nodes, the deleter and reason in a permanent form is necessary (and, I will add, already done, which is good). Deleted users warrant the same treatment as deleted nodes, perhaps a bit more. (I don't know if there's a deleted users node anywhere)

Borging someone is temporarily revoking someone's ability to speak in public. While necessary it is still subject to abuse and as such the information necessary to detect that abuse and the abuser (when it happens) is also appropriate.

There is some legitimate concern that the borg-ee may well decide to go on some sort of vengeance spree against whoever shut them up, but that's not particularly likely, the damage they can inflict is minor, and there are already mechanisms in place to deal with that damage. There aren't, so far as I can tell, many folks who're prone to vandalisim anyway, and of those who are I doubt knowing who was responsible for squelching them is going to make much of a difference in their actions. (And even if it does, as I said, there are mechanisms in place to deal with it)