I think his point was that, assuming that vegetarianism is ethical, hiding the abbattoirs etc may wind up increasing vegetarianism rates because when a sheltered meat-eater runs into them, they may be shocked into vegetarianism; while if everyone grew up raising their own pet chicken and slaughtering it themselves, no one would be shocked and they would all shrug upon seeing any video or photos.

I'm not sure this is true, since as the population urbanizes and specializes under economic growth, regardless of hiding animal suffering, people will inevitably not grow up slaughtering animals and will remain naively sensitive to suffering. So hiding then may increase the 'quality' of shock (more people who have no idea) but decrease too much the 'quantity' of shock (hidden means, well, hidden). But I have no idea how one would show this, and even if Goetz's suggestion turned out to be wrong, it's well worth remembering.