No League of Nations, or of individuals, can avail, without a change of heart. Reformers of all classes must recognize that it is useless to preach peace by itself, or socialism by itself, or anti-vivisection by itself, or vegetarianism by itself, or kindness to animals by itself. The cause of each and all of the evils that afflict the world is the same the general lack of humanity, the lack of the knowledge that all sentient life is akin, and that he who injures a fellow-being is in fact doing injury to himself. The prospects of a happier society are wrapped up in this despised and neglected truth, the very statement of which, at the present time, must (I well know) appear ridiculous to the accepted instructors of the people.

Seventy Years Among Savages (1921).