One common criticism of Marxism-based ideologies, such as Socialism and Communism, is that those who work will ultimately devote all their time to supporting those who do not work. This includes the ruling class that always develops despite Marxism attempting to remove any sort of class system, and people who understand that they will receive communal support no matter what and move from working to gaming the system.
Somehow it seemed as though the farm had grown richer without making the animals themselves any richer -- except, of course, for the pigs and the dogs... There was... endless work in the supervision and organisation of the farm. Much of this work was of a kind that the other animals were too ignorant to understand.
(Orwell, Animal Farm, msxnet.org)
The pigs, being more intelligent and understanding that Old Major's dreams are unworkable, instead use his ideas to place themselves into a ruling class that exploits the hard work of the other animals. Without any other authority, and with the threat of Napoleon's dogs, the animals are forced to work harder than ever without gaining any real benefits; in reality, every country that has attempted Marxist-based society has instead created a dictatorship in which the people work in poverty while the rulers prosper without working.