In addition to what is mentioned above, there was an idea that capitalism is or can be inherently unstable and that humans should not strictly be tied to the value which they bring to those for whom they work. Instead, resources are assumedly plenty and should be shared equally so that all people can profit from labor and pursue passions as well. He also argued that the society which you are in will change your world view: ie in capitalism a poor starving artist may be considered by and large a loser, whereas in his treatment of communism they would simply be an artist contributing art to society without negative inflection. It's important to note that during his tenure on planet earth when he was thinking about these things communism had started mostly as a movement within a small group of intellectuals, depending on where you live it has different connotations today.