We cook our meat mainly for two reasons, to break down the protein in the meat into amino acids for the flavor and more importantly, destroying any microorganism present in the meat. In the case of sushi and sashimi, raw fish presents a unique savory flavor from the fish oil which would otherwise be destroyed if subjected to high temperature. In order to maintain the flavor cooking of the fish is avoided. However in doing so it presents the other problem; the risk of infection on the meat.
Meat from a healthy animal is actually safe to consume. It is after all part of the animal. What makes uncooked meat unhealthy is what happens after the slaughter. Without the antibodies when it was alive, the meat is now susceptible to infection. Bacteria will begin to invade the meat and fungus from the external environment may even begin to grow on the meat surface. Hence Japanese fishermen takes additional precaution to prevent these infections when fishing.
