I've not quite pieced everything together yet, but based on what I have, the answer (I think) is
"A demon's numbered here about!"
This I'm not sure on. In the Bible, Jesus expelled a mute (dumb) demon from a man who was then able to speak. 666 is a triangular number and it's simple because it's a repidigit... No, I got nothing.
"You are a fool" The people shout!
"Simple" also means dumb (foolish)
The cure? A herbal remedy.
simple: n a medicinal herb, or a medicine made from one.
"the gatherers of simples"
That's no bad break
Simple fractures (broken bones) aren't as bad as compound fractures.
It's clear to see.
Self-explanatory, but something that is simple is obvious, i.e. clearly noticeable.
There's double trouble next, no doubt.
When something is simple, it is expected that something complicating is nigh.
Or maybe this random line I saw from the Bible: "The prudent see danger and take refuge, but the simple keep going and pay the penalty."
It makes me slip, impels me out.
I'm unsure about this one, but maybe... You mess up (i.e. slip) spelling "simple" and accidentally spell it "simpel?
The title "If you're minded to answer it"
If you're simple-minded, it may be too complicated. This goes along with "Clem," the simple-minded crawdad slappee who was mentioned in the original narrative.