No one is harder on those who sin than a convert who sins no more. Hence, former smokers who cannot stand being anywhere near people who smoke and anti-Leftists who used to be communists, like Whittaker Chambers.
David Horowitz is a case in point: he was a communist and radical in the 1960s, now he's a libertarian, free speech defender and anathema to the ivory tower liberalism that dominates academia and much of the Democratic party.
His new website is Discover the Network -- the groups and individuals who make up the American Left and the spiderweb of connections between those groups and people. He has a "guide" to the website here and admits that the website has made some mistakes and WILL correct those (he specifically notes the thumbnail biography of The Nation's Katrina Van den Heuvel and the corrections she requested, with which he complied).