One day the absurdity of the almost universal human belief in the slavery of other animals will be palpable. We shall then have discovered our souls and become worthier of sharing this planet with them.
Martin Luther King

Man is man because he is free to operate within the framework of his destiny. He is free to deliberate, to make decisions, and to choose between alternatives. He is distinguished from animals by his freedom to do evil or to do good and to walk the high road of beauty or tread the low road of ugly degeneracy.

The Measures of Man (1959)

The fact that man knows right from wrong proves his intellectual superiority to the other creatures; but the fact that he can still do wrong proves his moral inferiority to any creatures that cannot