that all communal leftist philosphies preach is sacrificing your needs and wants for the needs and wants of the greater good - well did you ever stop and look through history when there is perceived to be not enough for all in that greater good? That's when socialism turns to national socialism because people start acting off an ancient instinct to stick with their own, which when coupled with the ingrained doctrine of being for the whole and not for individuals taught from socialism, means they will have to be against certain groups.
Look at a supposed pure Socialist like Chavez, he has started talking more and more as things get worse about Venezueala being for Venezuelans when he does his nationalization. Though it's not too widely reported there are even in the past few years, reports of Jews being targeted by Chavez:
http://www.forward.com/articles/12500/