I think what it comes down to is if you keep a lot of animals in a small space, they can't engage in natural behaviours and if they are with unfamiliar other species, they're going to get sick. That's the bottom line. We can't manufacture our way out of it with technology and such.
Better welfare is the answer to better animal health, which is the answer to better people health. It's a very simple connection, and we have all the evidence that it needs to be addressed.