I feel like his lunacy was caused by JARED intentionally botching the surgery to steal his colon and getting away with it.
He was always a lunatic. But after that his twisted freak brain got focused like a Laser onto one specific asshole .
Fragile psycho's like mcdougal actually provide an import service unto society, they are little landmines laid out by God designed to punish you for stepping on them. You wrong a normal person cheat them, fuck them over, well they aren't going to be happy but you probably aren't in danger.
They might sue you, or complain, or report it or even just decide it's not worth it and move on, they have a civilized response that you can deal with in a civilized way.
The landmine psycho is completely different. You fuck with him and now you have to deal with him forever. He will carve your vermin name into his fucking skin and carry it around for eternity. He will think of nothing but hurting you. The pain you caused him or that he believes you caused him will bounce around in his head for all time until you're all he thinks about. the world is kept civilized by the normal person but it's kept polite by the psycho.
If there were no random landmines like Robert mcdougal just laying around you could walk on people all day every day and never have to actually be afraid. He provides a service.
A doctor will be scared of a review board or his premiums going up or having his licence suspended, but only in an intelectual way. Landmines frighten in a way that sticks better than any social or administrative punishment.