Is it safe to eat raw fish?
I discussed a similar subject in this question: What exactly is "Sushi Grade" fish?

Raw fish isn't safe to eat if it's just been sitting around.  However, the raw fish used in sushi/sashimi has been frozen (typically flash-frozen) in order to kill any parasites, making it as safe as any other food.

Most distributors of sashimi also have their own methods and internal regulations to ensure food safety, but specifics are understandably hard to come by.  Suffice it to say, it's far safer to eat properly-prepared nigiri or sashimi than it is to eat an undercooked hamburger.