Inasmuch as I am hardly a Marxist (as far as 19th-century philosophers go, I much prefer Mill), I feel I have to make the following points in the interest of fairness:
Ah, the classic "it didn't work so it wasn't really communism" defense. Of course this shouldn't improve one's perception of far-left economics, since all this demonstrates is that every attempt at Marxism has left countries devastated and totalitarian, as opposed to communism itself. Is that so much an improvement?
It's not so much that as the fact that Lenin hijacked Marxism before anyone actually attempted it. Lenin took the idea of the revolutionary vanguard from Blanqui, whom Marx regarded as a fool. Marx insisted that the revolution had to be prepared in a fully-industrialized country, which Russia definitely was not, and if you understand Marxism's fundamental point, you'll realize why: capitalism produces a bounty of great stuff--enough for everybody, in fact--but distributes it foolishly. He celebrates capitalism's ability to produce things and produce vast quantities of material goods. However, these things are produced in the interest of what produces the greatest profit rather than what people actually need; socialism and communism would supposedly remedy that maldistribution. Say what you like about the idea--its impracticality is one I particularly noted--but at the very least you have to recognize that it couldn't possibly have been established in Russia, or in China, or anywhere else that "Communists" have taken power. In Marx's view, capitalism has to be established and have reached its full productive capacity before anything else can happen. He gave more or less explicit advice to the Russian socialists that they ought to encourage the development of capitalism there before trying anything, and he actually applauded the British colonization of India for introducing the capitalist system to a country that he regarded as incapable of advancing otherwise. Engels said much the same thing about the bloody French suppression of rebellions in North Africa.
Thus there have been no attempts at Marxism as Marx understood it. Of course, that's partly his fault: despite his critique of capitalism, he really never got around to fleshing out his ideas on what was supposed to come afterward. He spent far too much time writing
Capital.
It really is baffling that people continue to defend Marxism to death these days. A 19th century antisemite, who inherited a great deal of wealth but nevertheless saw the wealthy as unconditionally evil, whose almost every prediction ended up not coming true, and whose philosophy of life is fundamentally based on the laughably insane G.W.F. Hegel, probably isn't end up going to be a prophet.
There are are a few things wrong here.
First, about Marx himself: he was not so much an antisemite as possibly a self-hating Jew; in any case, "On the Jewish Question" was written early in his career, before he formulated Marxism, and good cases are to be made (I'm not saying I necessarily believe them, but good cases they are) that that article has been misconstrued. Also, he was hardly rich, but rather comfortably middle-class in his childhood. He led a more or less hand-to-mouth existence in London, i.e. for most of his life (he had to rely on Engels' generosity--Engels, as it happens
was rich--to get by). Writing doesn't get you very much pay, you see.
Second, on Marx's ideas: First, Marx contributed a great deal to political and social thought, and his ideas have proven indispensable in the development of the social sciences. His emphasis on material social forces, despite its couching in Hegelian terms, informs virtually all contemporary study in political science and sociology. In that we are deeply indebted to Marx, even if he was probably overly simplistic in his dismissal of individuals and ideas in his analysis. We may not share his application of the Hegelian form to the general idea, but the idea had to start somewhere, and the concept can be seen as starting with Marx at least as much as with Comte. His critique of capitalism, although it is often dated or outright wrong, is nevertheless incisive, and deserves serious consideration by capitalists and anti-capitalists alike.
Of course, his attachment to Hegel is, frankly, rather silly, and ultimately it is that attachment that puts the lie to his predictions; they are founded on a theory of History that doesn't necessarily follow from his premises.
As for the dictatorship of the proletariat (which has been bandied about a bit), he never gave a clear indication of what he wanted, which is why self-proclaimed Marxists have been able to declare whatever they wish "Marxism" when in fact Marx is probably spinning in his grave on account of them. The only thing he ever seriously said about it is in "The Civil War in France," in which he indicates that the dictatorship of the proletariat would look a lot like the Paris Commune, only for more than a few months in the spring, in more than just one city, and with a couple of changes made.
As to the overall question of the thread: the conflation of socialism and communism in the United States is really a historical matter (duh) that has to do with the fact that socialism has never really had a foothold in this country. It's easy to misunderstand that which with you are unfamiliar: unlike Europe, the socialists failed to establish a strong connection with the mainstream labor unions, so when the workers' movement got a foothold, it didn't have a socialist flavor but rather a liberal, progressive-reformist one--one that meshed well with the existing political parties. At the end of the day, the unions hitched their wagon to the Democratic donkey rather than the GOP's elephant for various reasons (the most likely being the association of the Republicans with the Northeast and thus industrialists), and socialism as such was effectively dead in America.
Now
why socialism never linked up with the unions in the United States is another matter entirely; it's certainly not for lack of trying. I've heard all kinds of arguments, none of which are entirely satisfactory.