"But when we first read The Communist Manifesto or Capital, Marxism seemed like a great idea, too. In reality, of course, communism turned out to be a nightmare, providing neither equality nor freedom to its people."

MSW, this is a rather facile statement:  rhetorically it makes your point, but only because it appeals to the canard that Marxism=Soviet Communism.  As most scholars of the field (and not just leftist scholars) will tell you, you have to draw an clear distinction between the ideas of Marx himself and their later development:  one of which was Soviet style communism, but there are other schools of non-authoritarian Marxist thought.  When discussing Marx himself (e.g., the Manifesto or Capital) it is customary to refer to Marxian ideas--most of which were a critique of capitalism and almost none of which were about "communism", however defined.