I found a similar quote, attributed to Tony Benn "It’s the same each time with progress. First they ignore you, then they say you’re mad, then dangerous, then there’s a pause and then you can’t find anyone who disagrees with you." http://www.bartleby.com/66/64/6664.html (from The Columbia World of Quotations, 1996)

I don't have the novel It Can't Happen Here by Sinclair Lewis, published in 1935 to verify the quote, but since a few different web sources of the quote reference that book I'd feel pretty good about quoting it. http://worldcat.org/oclc/288938