Alright, so let me clarify a bit since I'm the mod in question here.
I was doing a ban for someone. Among other issues were some objectionable posts on their walls.
When you ban people, there's a little box that says "Delete PMs and Walls". So... thinking this would delete PMs and walls, I thought "oh, well that seems appropriate for this situation, I'll do just that".
Unbeknownst to me clicking that box actually deletes every post they've made, and apparently some posts that quote them as well.
There's a possibility that I may have used that on other users too, if this has happened before. Like, John requested a ban, so I figured he'd want his walls wiped clean too. Now that I know that clicking the box doesn't do what I thought, I won't be clicking it anymore.
So, this was not an effort to delete posts. I legitimately had no idea that was even something I could do, and was as surprised as anyone else. I think they're working on changing the way that option works so it won't be an issue in the future.