The point that people are trying to argue here is that Marx himself felt that there was always bloody struggle to implement social change. There were several 'phases' of political change that he defines. I can't remember them all (last time I read this stuff was Philosophy 101, Feudalism was probably one of them), but currently we are on "Democracy/Capitalism". The next stage would be "Socialism" and then "Communism." He viewed transition between stages as only coming about through bloody revolution.
Side Note: While people like to say "Socialism == Communism", Marx viewed them as separate and distinct 'stages' of political/economic development.
Actually, in the original German, Marx used the words Socialism and Communism interchangeably in many of his writings. (Kommunismus and Sozialismus) It was Vladimir Ilyich Lenin who first differentiated between the two and started using socialism to refer to a transitional state between "lower" and "upper" Communism.
Of course, the socialism that most people refer to doesn't correlate with any correct definition (more closely "democratic socialism"), but what do we expect from the "unwashed masses". ;)
Sweden is a socialist state, and a family is a commune.
Just because ideas have failed spectacularly in some places and on some scales doesn't mean they don't work well elsewhere.