Once I was a socialist, but now, now I am a communist. For anyone unsure of the differences in economic systems, courtesy of the most marginally reliable encyclopedia:
Capitalism is an economic system in which the means of production are privately owned and operated for profit, usually in competitive markets.
Socialism is an economic system in which the means of production are publicly or commonly owned and controlled cooperatively, or a political philosophy advocating such a system.
Communism is a sociopolitical movement that aims for a classless and stateless society structured upon common ownership of the means of production, free access to articles of consumption, and the end of wage labour and private property in the means of production and real estate.
So, Capitalism involves control by the rich, Socialism involves control by a democratic state, and Communism involves control by the workers organized in collective. Capitalism and Socialism can exist in a state, while actual Communism is a world, classless, stateless society.
I don't think I'd be Communist if I just cared about the US, but the system of exploitation across the world, involving so many starving and dying poor, compels me to the extreme.