I don't think pointing to the failings of communist regimes in fields of human rights and so forth is enough to discredit communism as a whole, much less Marx's views. If it was, we'd only have to do the same thing to capitalist societies to entirely discredit capitalism, and where would that leave us? Stalinism is far from the only ideology, ah, loosely based on classical Marxism. There's nothing about Stalinism that really discredits Marx's theories, and I think you'd have a difficult time finding a political theorist more influential than Marx in the past couple of centuries. The fact his theories are only becoming more relevant as we have moved more and more toward a global capitalist system, just serves to underline this fact.
I think there's a tendency among typical westerners to exaggerate the evils of communism. The Soviet Union, Democratic Kampuchea and communist China - there are plenty of horrific examples from those places. There are also several countries that are very rarely mentioned. Other examples are less extreme, but they had their own problems. I'm just not convinced that these were necessarily worse than the problems faced by groups in many western countries up until very recently, or even today. Looking at the long list of CIA crimes, treatment of African Americans and homosexuals until today, the prison-industrial complex - I think you'll find that abuses of civilian populations are not strictly a communist thing.
For that reason, I think I'd like to add to the list of annoying historical myths the idea that a better society than the one we currently live in is not possible. I very much doubt this is the first time people seem to think they live at the end of history, and it would take a staggering amount of arrogance to assume that this time it's correct. It just seems that way because not many people have the imagination to think of working alternatives, and even fewer have the capacity to put those ideas into practices. And, unfortunately for us, most of those that do, probably live in places that are effectively under the control of people who are very much opposed to alternatives.