A quote from Jane Eyre that I really like (found on another site):

If people were always kind and obedient to those who are cruel and unjust, the wicked people would have it all their own way: they would never feel afraid, and so they would never alter, but would grow worse and worse. When we are struck at without a reason, we should strike back again very hard; I am sure we should -- so hard as to teach the person who struck us never to do it again."
-- Charlotte Bronte, Jane Eyre

(I don't remember this quote, but I used to really like the book. I should re-read it sometime and see if it still appeals to me.)