The problem with this is that capitalists can use the same argument and say that past capitalist crimes or faults were not true conservatism or classical liberalism or that the crimes of present day capitalists are not representative of conservative ideology, and so on.
The Russian revolution was the closest thing to the Marx and Engels Manifesto, and although the USSR's egalitarian style has never been matched by any western liberal democracy, the tyranny was wrong.
Yes, to reiterate what Blake had stated above, the USSR and China were state capitalist societies. Capital takes many faces: nationalism, fascism, state capitalism, etc. Marx laid out some basic requirements in Das Kapital in order to transcend capital (which is a social relation, not a "thing" meaning that it is mediated by everyone who exchanges and participates in the labor market). From my knowledge, Russia only substituted one type of bourgeoisie for another.
This has been something I've been arguing on other threads, and it is that a "party" can serve the same function as a less-formally arranged bourgeoisie can. Marx didn't want to have surplus value/profit to simply be siphoned-off by less harmful means, because that entirely ignores the fact that surplus value extraction is not harmful to begin with. As I previously mentioned, capital is not simply money--it is you and me. We're capital every time we go to work for a boss. We're engaging with capital when we buy or sell. To assume then that a place like Soviet Russia or China was absent of these relations is patently false: there economies did compete in the global commodities market.
Some people, out of their impatience and lack of reading Marx's critique of political economy often bemoan this position (which is in the minority). They want the grandeur, they see themselves as romanticized revolutionaries, educating the masses who have yet to be enlightened. These are bourgeois fantasies and are unfortunately pervasive. One must keep in mind that Marx labored for over 50 years trying to demystify the world of the bourgeoisie and the economic foundation which supports them--capitalism. In the end, he determined that the potential for any material change in the world would come from the direct experiences of the work him/herself, only they could unleash the material forces to destroy and create the capitalist order. All previous attempts--while noble, I might add--have unfortunately fallen short of their revolutionary potential precisely because of the issue of consciousness and a compromised state of affairs.
"Even mistakes which a truly revolutionary labour movement commits are, in historical perspective, immeasurably more fruitful and valuable than the infallibility of the very best ‘central committee’."
- Rosa Luxemburg