>Or is it just because the mods jerk off to it that its allowed to stay?
That's not the only reason they are allowed.

>even though he makes needlessly annoying and disgusting copypasted /b/ threads about eating shit every week?
First of all, there is no rule against "needlessly disgusting posts".
From what I could gather with search engines is that his threads (this is the second I remember of, the other one was several months if not over a year ago) about his sister's poop are original content. You claim his posts are repulsive thus annoying you, but I think that's just a little better than someone claiming our lolicon posts are ethically wrong & noone finds them good and thus made just to annoy users.

There was another user who was just posting their own feces on Off-Topic as well, and I did delete their threads when I deemed it was getting too frequent and started to annoy users who initially enjoyed the threads.

Attacking OP by posting "Go fuck yourself weirdo." is Rule 8, there is no use in arguing about this. You can make negative posts (like 98723-kun did, although it's worth noting he is a certain ban evader too) when you don't like the content, that's really another story.