So this butcher was standing in his insufficiently cleaned butchering room telling you about how he should really be doing what industrial slaughterhouses do, but he just can't be bothered? Or did he have his own methods of sufficiently sanitizing his workspace such that he wasn't a source of disease and poisoning?

What volume brings is increased odds of one of them introducing/reinforcing a contaminant, especially if they're from a CAFO, which are horrifically unsanitary. Again, there's a reason industrial operations have apparently higher standards. When Mad Cow disease was spreading, it wasn't because a local butcher was lax wiping things down, it was because cow brains were being recycled into cow feed and sold across North America on an industrial scale.