By describing how people would live if everyone adhered to the socialist ethic, utopian socialism does three things: it inspires the oppressed to struggle and sacrifice for a better life, it gives a clear meaning to the aim of socialism, and it demonstrates how socialism is ethical, that is, that the precepts of socialism can be applied without excluding or exploiting anyone.
The problem with Utopian socialism is that it does not concern itself with how to get there, presuming that the power of its own vision is sufficient, or with who the agent of the struggle for socialism may be, and, instead of deriving its ideal from criticism of existing conditions, it plucks its vision readymade from the creator’s own mind. Over 40 versions of Utopia were published between 1700 and 1850. Engels makes special mention of Morelly’s Code of Nature
See also Utopia in the Encyclopedia of Marxism.