Sectors: Private & Public, comparison

What can the public sector do? Can extra gov spending help the economy?  Unemployment has been at almost 10% for a year, well over the worst 8% projected, without the Stimulus. There was suppose to be a lot of infrastructure projects, but those came to about 5% of the total. It actually seems that the Porkulus Package was engineered to NOT create value. Much was for political payback and generate ditch digging & filling jobs. How can $800 billion be spent (really about 75% of that, now) and NOT produce much?