Slaugherhouses and similar lines of work change a person for the worse. Institutionalized killing makes workers often numb and more prone to all forms of violence. PTSD is common as well. Near universal dairy industry practices include things like killing cows after their productivity declines, separating calves from mothers, and more. Some quotes from workers in slaughterhouses I think describe what those kinds of things do to a person most aptly

“Maximum six months then you make a change, because if he shoots continuously it will start affecting him. He gets a murderous attitude in him. He will do it to other people. He will stab you with a knife, turn around and walk away.”

[...]

"As time passes, you get used to it. You feel nothing. You can imagine, if you kill a thing a 1000 times over and over, you wouldn't have feelings after a while. It kills you on the inside, an abattoir, it kills you. You can be full of blood, it will not bother you"

https://pmc.ncbi.nlm.nih.gov/articles/PMC4841092/

Here's another

Down in the blood pit they say that the smell of blood makes you aggressive. And it does. You get an attitude that if that hog kicks at me, I’m going to get even. You’re already going to kill the hog, but that’s not enough. It has to suffer.

https://theconversation.com/animals-suffer-for-meat-production-and-abattoir-workers-do-too-127506