There is an interesting letter from Rav Kook to his son [also known, oddly enough, as Rav Kook]. There was a period when his son was a vegetarian and his father asked that he not let it affect his health. He also told him not to be swayed by animal rights activists, many of whom HATE people and care only about animals.
This past Motzei Shabbos, at the melave malka tisch, the Rebbe Shlita related that when he was young he read the memoirs of a certain Nazi. This Nazi would write in his diary daily with satisfaction how many people he had sent to their deaths. 500, 1000, 2000 - Kol hamarbeh harei zeh meshubash [in his twisted, evil mind]. He never shed a tear or expressed guilt.
Then a "tragedy" befell him. His beloved dog was "niftar". It was extremely difficult for him to deal with the loss. Then he did something he never did for the thousands upon thousand of Jews he tortured and killed.
He cried.
Zachor eis asher asah licha Amalek. Yimach shmom vi-zichrom li-olmei ad!!!