What someone calls themselves and what they actually are don't always match up.

Socialism in Germany was a middle-class tendency that was frequently co-opted by right-wingers. The German Communists tried to fight against this, but the Social Democrats sent in the Freikorps to kill them. So yeah, some German socialists abandoned their principles to become fascists while the Communists got killed and were later put into concentration camps. Not a good example, because it ignores every other piece of history that went into that story.