If we are socialists, then we must definitely be anti-semites - and the opposite, in that case, is Materialism and Mammonism, which we seek to oppose... How, as a socialist, can you not be an anti-semite?
The reason Hitler, and Marx (despite his Jewish heritage) were anti-Semitic is that Jews were the money-lenders and thus controllers of capital. Add to that the evolutionary theories that breed racial superiority complexes and you come up with anti-semitism. You can’t be a leftist without being an anti-Semite.