A single counterexample would disprove this

Go ahead.

Torture factories don't exist

What do you mean? It sounds like torture to me: "Chickens raised for meat have been genetically selected for rapid growth. They typically reach market weight 6–7 weeks after hatching and grow so fast that their organs and bones often cannot keep up. As a result, many die from heart failure or other ailments, and countless more suffer from broken bones, lameness, and ruptured organs."

Many more kinds of torture are documented by this and many other sources that are easy to find.

I don't know how you can prove this

Here's the data.