Jacob, thank you for making some very good points. The only problem I have with your argument is your analysis of Leninism. Specifically, that compromise would work. Lenin's interpretation of communism hinged its very existence on the destruction of social classes, the construction of the dictatorship of the proletariat, etc. The liberals and moderate socialists you mention would be highly unlikely to want such a change of social order, and thus they would be about as suitable as allies as the extreme capitalists.