Anarchism can be seen as a form idealist socialism. I also think it can be seen as a limited world view. Anarchists have the same end goal and the same enemy as us, same God and Devil, if you will, but they have far less in the middle.
Marxists study the complexities of class relations. Compare the Manifesto to something like the Wobblies' membership guidelines, rather simplistic--anyone without the power to hire and fire. Likewise, their view of history, even when not riddled with liberal lies and misinformation, has a binary classification. They rightly identify the USSR as not having achieved a classless and stateless society of abundance and point to that as a fault, but are unable to see that for its faults, the USSR was a net good because it improved the lives of Russians, Asians, Europeans, and Third-Worlders (in the economic, not 3-World-Theory sense). For the time and conditions, it was amazing. They get too hung up on the civil liberties too sometimes. Make no bones about it, though, the USA had only marginally freer freedom of the press and that was only available to those who owned a press. Additionally, now that the 99% are waking up and actually present a threat, the bourgeois states are identifying which forms of expression are bad and cracking down on them.