A human being is a part of the whole called by us universe; a part limited in time and space. He experiences himself, his thoughts, and his feelings as something separate from the rest - a kind of optical delusion of consciousness.
The indifference, callousness and contempt that so many people exhibit toward animals is evil first because it results in great suffering in animals, and second because it results in an incalculably great impoverishment of the human spirit.
Apart from selfish reasons, such as fear of punishments, fear of blame, of dishonour, etc, there remains only two motives that can stop (or prevent, "empâecher", Fr.) men from acting badly; the natural sense of commiseration (or "sympathy", - "commisération", Fr.) for one's fellow men - compassion, and the influence of education, by association of ideas ("par l'association d'idées", Fr.) - habit.
Criminals, people who commit crimes, usually society rejects these people. They are also part of our society. Give them some form of punishment to say they were wrong, but show them they are part of society and can change. Show them compassion.
And were your back as broad as heaven, and your purse full of gold, and did your compassion reach from here to hell itself, there is nothing you can do.
If one doth act in friendly wise, With no evil thought toward any single creature, And in so doing becometh proper, And if he have compassion in his soul Toward all living beings--this noble one Doth acquire abundant Virtue.
Be guided, only by the healer of the sick, the raiser of the dead, the friend of all who were afflicted and forlorn, the patient Master who shed tears of compassion for our infirmities. We cannot but be right if we put all the rest away, and do everything in remembrance of Him. There is no vengeance and no infliction of suffering in His life, I am sure. There can be no confusion in following Him, and seeking for no other footsteps, I am certain!