Communism and socialism are ideas that are just so elegant, simple, and appealing, that they'll never go away.
Even if you drove every vestige of them out, someone would inevitably think of them again.
Anyone who wonders how to improve the world inevitably comes to some form of these systems.
And it's hard for me to believe that so many humans--who've been mentally conceiving solutions to problems, then executing them, for at least as long as language has been around--can be wrong-headed; that the whole concept is utopian.
We can see it clearly in our heads: a post-scarcity society with no rulers, with resources divided equally, driven by needs rather than an addiction to constant growth, with everyone having access to land or a domicile, etc.--it's not hard to imagine.
But there's a large minority of people with highly-vested interests in making it seem impossible--in sabotaging it; in dividing people.
It's harder for me to believe them than it is to believe in a better world.