“Human love is not love. Love is natural to every body but it becomes human love as the person learns from society to confuse love with sex.”

Sex
Source: "I am That." P.111.

The portion of this statement, "Love is the only sane and satisfactory answer to the problem of human existence" has been widely quoted alone, resulting in a less reserved expression, and sometimes the portion following it has been as well: "Any society which excludes, relatively, the development of love, must in the long run perish of its own contradiction with the basic necessities of human nature."
The Art of Loving (1956)
Context: Our society is run by a managerial bureaucracy, by professional politicians; people are motivated by mass suggestion, their aim is producing more and consuming more, as purposes in themselves. All activities are subordinated to economic goals, means have become ends; man is an automaton — well fed, well clad, but without any ultimate concern for that which is his peculiarly human quality and function. If man is to be able to love, he must be put in his supreme place. The economic machine must serve him, rather than he serve it. He must be enabled to share experience, to share work, rather than, at best, share in profits. Society must be organized in such a way that man's social, loving nature is not separated from his social existence, but becomes one with it. If it is true, as I have tried to show, that love is the only sane and satisfactory answer to the problem of human existence, then any society which excludes, relatively, the development of love, must in the long run perish of its own contradiction with the basic necessities of human nature. <!-- p. 111 - 112

Source: War and Peace

Source: Dhalgren

Living in Harmony (2000)

Graziella (1849), Pt. IV, ch. 5

1990s, Long Walk to Freedom (1995)

https://twitter.com/BarackObama/status/896523357272911872 Speaking via twitter on August 13, 2017 in response to the 2017 Unite the Right rally in harlottesville, Virginia and quoting Nelson Mandela. Archived via Wayback Machine on August 14, 2017 https://web.archive.org/web/20170814133749/https:/twitter.com/BarackObama/status/896523357272911872. Source: Bipartisan condemnation for 'Unite the Right' rally by CNN's Jennifer Hansler on August 13, 2017 http://edition.cnn.com/2017/08/12/politics/parties-condemn-white-nationalist-rally/index.html. Archived via Wayback Machine on August 14, 2017 https://web.archive.org/web/20170814134330/http://edition.cnn.com/2017/08/12/politics/parties-condemn-white-nationalist-rally/index.html.
2017
Variant: Madiba reminds us that: “No one is born hating another person because of the color of his skin, or his background, or his religion. People must learn to hate, and if they can learn to hate, they can be taught to love, for love comes more naturally to the human heart.”