Why should we change to socialism?

This is the most powerful country in the world, and we have gotten that way through capitalism. Everything is going fine except for the wars and the economic downturn, and we want to spend MORE money? It really just doesn't make sense to me. Why should we change from something that succeeds and has managed to create the greatest country in the world, and go to something that has made the poorest countries? (I.E. Cuba, Venezuela, North Korea, etc.)