"If slaughterhouses had glass walls, everyone would be a vegetarian"

In this quote, Paul McCartney is suggesting that if people had the ability to see the procedure of how animals are slaughtered in slaughterhouses, they would be more likely to become vegetarians. He is suggesting that the reality of the harsh and frequently inhumane treatment of animals in these facilities would suffice to turn individuals away from taking in meat. By using the metaphor of "glass walls," McCartney is highlighting the concept of openness and visibility, suggesting that if individuals were able to witness the reality behind the meat industry, they would be more inclined to make ethical and thoughtful choices.