A political and economic system that has been completely and utterly discredited (most notably by the emininent Austrian economist Ludwig von Mises.)
Sadly, many people, being generally ignorant of the laws of economics, are unable to come to terms with the fact that socialism, unlike free-market capitalism, is economically incapable of generating wealth and thus can only ever impoverish any existing society when implemented.
Many people are also of the opinion that socialism, while a good idea on paper, can never work in reality purely because of human selfishness, and not because of the afore-stated economic reason. These people are quite possibly the biggest culprits when it comes to holding back human social development, as they persist in blinding countless people to socialism's true shortcomings. (American colleges, for example, are hotbeds of left-wing propaganda.)
Ardent supporters of socialism are usually bitter, twisted individuals who hate life and everything it stands for. They often have an insatiable God-complex and, remaining deliberately blind to the existence of genuine altruism and compassion, wish to destroy humanity as it exists and remodel it in their own image.
Tell your kids to say "No" to socialism.