Socialism can't work because we are human. Any time a government holds the strings of an entire society's economic system there's bound to be some form of corruption. It's impossible to have a 100% benevolent socialist government.
Pretty much what Shwolli said.
Also, in response to what Bisjac said as I was posting, there is no perfect form of government. There will always be some way that someone finds to forget it up somewhere along the line. However, with socialism and an economy controlled by the government, you know what else the government controls? The military. Taxes. Our healthcare. Our education. The private sector cannot control everything that the government controls at once. It's not a perfect system, but it's better than socialism.
Well...
Socialism, in certain degrees, can work. It's different than just straight up communism. It's a mixed economy, meaning the market is still free, but everything else is government controlled.
A great example is France, or Britain. They've had socialism for quite some time now and they still exist, and are thriving. It's just how you handle the situation, and make sure you apply the correct means.
Edit:
Yeah, you pretty much described everything we are. The private sector doesn't control that, and socialism makes sure of that as well. Socialism isn't the evil here, it's the people running it we should worry about.