If a chihuahua attacks me, I could kill/subdue it with a squeeze of its neck by my hand. If a pit attacks you it's either curtains or surgery. If you want to use a gun analogy, then think semi-auto and auto weapons. Certainly all breeds bite. But here in Cook county Pits are responsible for the majority of bites and they often cause massive damage.

As for eugenics, these are animals, not humans.