“Ideas consume the ages as passions consume men. When man is cured, humanity may possibly cure itself.”

Source: The Death of the Liberal Class

"Why I Am So Wise", 6
Ecce Homo (1888)

Fischerisms (1944)

Ein Mensch wie ich kann ohne Steckenpferd, ohne herrschende Leidenschaften, ohne einen Tyrannen in Schillers Worten, nicht leben. Ich habe meinen Tyrannen gefunden und in seinem Dienst kenne ich kein Maß.
Letter to Wilhelm Fliess (1895), as quoted in Journal of the History of the Behavioral Sciences Vol 3-4 (1967) p. 159
1890s
Context: A man like me cannot live without a hobby-horse, a consuming passion — in Schiller's words a tyrant. I have found my tyrant, and in his service I know no limits. My tyrant is psychology. it has always been my distant, beckoning goal and now since I have hit upon the neuroses, it has come so much the nearer.

Comparable to remarks of William Masters, in "Two Sex Researchers on the Firing Line" LIFE magazine (24 June 1966), p. 49: "Science by itself has no moral dimension. But it does seek to establish truth. And upon this truth morality can be built."
Variants:
Science does not have a moral dimension. It is like a knife. If you give it to a surgeon or a murderer, each will use it differently.
As quoted in Futurehype: The Myths of Technology Change (2009) by Robert B. Seidensticker
Science does not have a moral dimension. It is like a knife. If you give it to a surgeon or a murderer, each will use it differently. Should the knife have not been developed?
As quoted in Science & Society (2012) by Peter Daempfle, Ch. 6, p. 97<!-- also in Good Science, Bad Science, Pseudoscience, and Just Plain Bunk: How to Tell the Difference (2013) by Peter Daempfle, Ch. 9, p. 166 -->
Responsible Scientific Investigation and Application (1976)
Context: One of the most disconcerting issues of our time lies in the fact that modern science, along with miracle drugs and communications satellites, has also produced nuclear bombs. What makes it even worse, science has utterly failed to provide an answer on how to cope with them. As a result, science and scientists have often been blamed for the desperate dilemma in which mankind finds itself today.
Science, all by itself, has no moral dimension. The same poison-containing drug which cures when taken in small doses, may kill when taken in excess. The same nuclear chain reaction that produces badly needed electrical energy when harnessed in a reactor, may kill thousands when abruptly released in an atomic bomb. Thus it does not make sense to ask a biochemist or a nuclear physicist whether his research in the field of toxic substances or nuclear processes is good or bad for mankind. In most cases the scientist will be fully aware of the possibility of an abuse of his discoveries, but aside from his innate scientific curiosity he will be motivated by a deep-seated hope and belief that something of value for his fellow man may emerge from his labors.
The same applies to technology, through which most advances in the natural sciences are put to practical use.

Tel est le malheur de notre siècle, les plus étranges égarements même ne guérissent pas de l'ennui.
Vol. II, ch. XVII
Le Rouge et le Noir (The Red and the Black) (1830)

§ 5
From Lives and Opinions of the Eminent Philosophers by Diogenes Laërtius