I think it's because the situation tends to get so absurd for the people who are now expected to work hard without reaping any benefits, that the only way to keep a system like that going is the force of violence. Thus a totalitarian regime (ala North korea) is necessary.
I'm not saying that Traditional socialism is perfect, or anything to defend it. I am simply letting everyone know that when they say "Socialism", usually they mean "Communism".