I guess even the SDMB must give the Devil his due, in a sense. President Warren G. Harding, to his credit, appointed former president Taft as Chief Justice; he also granted a Presidential pardon to the high-minded socialist Eugene V. Debs, who had been grossly deprived of civil rights in the events leading up to Debs’ incarceration.
Please post here incidences of someone best known as a villain, doing something positive, constructive–well, you get the idea. 
Um, Hitler helped bring about Volkswagens? Cliched, I know, but the first thing I thought of.
Nixon helped open the doors to communist China.
Senator McCarthy helped us to realize how destructive and stupid it is to go witch-hunting.
I understand that Hoover actually advised President Roosevelt NOT to detain Japanese-Americans during World War II. He felt they were not a threat to national security.
Preston Manning believes in recall votes and an elected senate.
William Saffire’s grammer column in the New York Times Magazine. I may disagree with pretty much all his politics, but it’s a damn good column, and very useful for grammar questions…
Back to Hitler…he DID commit suicide.