A funny idea came to me the other day. Karl Marx would not have supported socialism from the moment he saw it not working. He was too intelligent. Socialism from him was sort of a "Jules Verne" attempt to guess the economic future -- or his economic "Brave New World."
He did a pretty good job figuring out what what wrong with the LABOR MARKET (I use all capitals hoping the word will be even noticed because it seems hard to get the concept even thought about for more than three seconds in intellectual circles) already (haven't read "Das" yet, but will now that this makes him seem potentially credible). He was just not very good at guessing the future.
He was not an ideologue like many later followers who take his "predictions" of common ownership of production for "revealed" religion. He had noticed (according to one comment on Economists View) that America did not need socialism because it had labor unions. I guess he lived in a world that was so totally different from today's (dominated for millenia by royal families -- only recently replacing muscle power with carbon fuel) that he just couldn't see the eventuality of labor organized democracies (today that can only be accomplished via legislated sector-wide labor agreements).
Marx would was too intelligent to have been a Marxist ideologue. He would instantly have recognized what even below average intelligences could easily diagnose was wrong with Communism in 1917.