“The idea of painless, non-threatening coercion is an illusion. Fear is the inseparable companion of coercion, and its inescapable consequence. If you think it your duty to make children do what you want, whether they will or not, then it follows inexorably that you must make them afraid of what will happen to them if they don’t do what you want.”

A Conversation with Ward Cunningham (2003), Working the Program

Quoted in "The Military Quotation Book" (2002) by James Charlton, p. 60

Source: The Crimson Crown

Variant: Fear again. If you want to control someone, all you have to do is to make them feel afraid.
Source: The Devil and Miss Prym

This saying is not found in any source before 2010, when it was posted by The Ignorant Fisherman at Free Republic http://www.freerepublic.com/focus/bloggers/2451682/posts on 15 February. The language is not that of Washington or his time.
Misattributed, Spurious attributions

1920s, Truth is a Pathless Land (1929)
Context: Your prejudices, your fears, your authorities, your churches new and old – all these, I maintain, are a barrier to understanding. I cannot make myself clearer than this. I do not want you to agree with me, I do not want you to follow me, I want you to understand what I am saying. “This understanding is necessary because your belief has not transformed you but only complicated you, and because you are not willing to face things as they are. You want to have your own gods – new gods instead of the old, new religions instead of the old, new forms instead of the old – all equally valueless, all barriers, all limitations, all crutches. Instead of old spiritual distinctions you have new spiritual distinctions, instead of old worships you have new worships. You are all depending for your spirituality on someone else, for your happiness on someone else, for your enlightenment on someone else; and although you have been preparing for me for eighteen years, when I say all these things are unnecessary, when I say that you must put them all away and look within yourselves for the enlightenment, for the glory, for the purification, and for the incorruptibility of the self, not one of you is willing to do it. There may be a few, but very, very few. So why have an organization?

LiNK’s Hannah Song: Forever Committed to a Cause https://web.archive.org/web/20160414025408/ttp://www.mochimag.com/article/links-hannah-song-forever-committed-to-a-cause (2010)

2000s, To Live Beyond Our Fear (2007)
Context: The thing that I want you all to remember: please, please, don’t base your vote, this time, on fear. Base it on possibility. Think. Listen. The game of politics is to make you afraid so that you don’t think. And what we need right now isn’t political rhetoric, it isn’t game-playing. We need leadership; we need people with judgment; we need decent people, people with common sense, people with strong family values. People who understand the world.