Why isn't it safe to eat raw chicken?
You can have raw chicken in restaurants in Japan - it's delicious.  Depending on where you live there may be better or worse food safety standards, but there is nothing poisonous about raw chicken itself.

By the way, sushi is a dish with vinegary rice.  The raw-meat dish is Sashimi. A picture of chicken sashimi:



You will note that in this photo the chicken is actually not raw but quite rare. The exterior of the chicken flesh is actually seared and cooked through several millimeters.