“It is a waste of energy to be angry with a man who behaves badly, just as it is to be angry with a car that won't go. The difference is that you can compel your car to go to a garage, but you cannot compel Hitler to go to a psychiatrist.”

Though Keillor has been quoted on the internet and in print as having made this or a similar remark, such expressions have been made by others, and may have originated with Billy Sunday, who is quoted as having said "Going to church on Sunday does not make you a Christian any more than going into a garage makes you an automobile!" in Press, Radio, Television, Periodicals, Public Relations, and Advertising, As Seen through Institutes and Special Occasions of the Henry W. Grady School of Journalism (1967) edited by John Eldridge Drewry.
Disputed

Gary Player – Great Golfer, Better Human Being, WorldGolf.com, Kyle Dalton, 2008-12-09 http://www.worldgolf.com/course-design/gary-player-profile.htm,

As quoted in "Return of the time lord" in The Guardian (27 September 2005)

Carlin on Campus (1984)

“Really?” I asked, drily. “Aren’t you getting tired of that?”
Source: Ancillary Justice (2013), Chapter 15 (p. 232)

Source: The Portable Atheist: Essential Readings for the Nonbeliever

Source: Focal Point: A Proven System to Simplify Your Life, Double Your Productivity, and Achieve All Your Goals

Though Keillor has been quoted on the internet and in print as having made this or a similar remark, such expressions have been made by others, and may have originated with Billy Sunday, who is quoted as having said "Going to church on Sunday does not make you a Christian any more than going into a garage makes you an automobile!" in Press, Radio, Television, Periodicals, Public Relations, and Advertising, As Seen through Institutes and Special Occasions of the Henry W. Grady School of Journalism (1967) edited by John Eldridge Drewry.
Disputed
Variant: Going to church no more makes you a Christian than standing in a garage makes you a car.

Never Scared (HBO, 2004)