Because everybody makes a mistakes, whether it is children, animals, or even you. And speeding is another mistake. Wouldn't it be prudent for the driver to go the speed limit or take precautions to slow down rather than spend the rest of his life regretting taking the life of a child, animal or a loved one.
How would you feel if it was your child or animal? Besides, why be in such a rush, life to short, don't make it shorter. And the life you're saving today, may be yours tomorrow--we all make mistakes.