I think its worth pointing out that, as far as I understand it, the "scientific" part of Marx/Engel's project does refer directly to the scientific method. Their goal was to establish certain universal, empirically-derived (in other words, scientific) laws of historical development which could then be applied to understand the rise and eventual fall of capitalism. In fact, in one of his intros to socialism: utopian and scientific Engels actually mentions Darwin, as well as LaPlace, as precursors to their project. Which gets to the real differentiation they attempted to make between themselves and the "utopians": Its not that these socialists believed in some magical society where everyone always gets along, its essentially that they attempted to resist the development of capitalism, to slow it down and essentially "opt out" of it by establishing non-capitalism communes and projects within a broader capitalist economy. Marx and Engels attempted to surpass these socialists by demonstrating that human civilization followed certain laws of development (increasing productive abilities and organization, intensifying class struggle / simplifying class structures, etc.) which meant capitalism could not be "opted out" of or resisted, only eclipsed by a new mode of production. Which is all well and good, but leads to some difficult problems when you really start looking at the necessary conclusions. There are of course other aspects of Marx's work that are really admirable and useful, but their whole project of making a science of history or revolution seems like a false start