I believe you're correct as a matter of old school Communist ideology. Class struggle is an amoral battle between classes asserting their interests. Old style socialists and communists seem very different to me than their modern day US counterparts, who more explicitly justify their arguments on moral grounds.

I'd argue, however, that Marx and Marxism are shot through with moralisms, starting with the Labor Theory of Value, Surplus Value, etc. Any theory of Objective value is implicitly a morality.