If we just took more money out of the private sector and put it in the public sector, the economy would improve?

Imagine if I I came to you with a gun, pointed the gun at your head, and said "Give me your money. I am going to hire lots of people to do things for me.  This is a good thing, and it will create more jobs." 

You would understandably think that I was stark, raving mad. 

You would say "Hey, Whited, my money is in the bank.  The bank is loaning it to companies and firms and individuals.  They're already creating jobs with my money.  That's the only way the bank can earn the interest that they pay me.  Put down the gun.  Jobs are being created at the same rate you could create them with my money." 

Imagine if I said "No, if I take your money, and hire people who overwhelmingly support me, it will create more tax revenue." 

I can hear you now, stating vehemently that you know the best use for your money, and that I'm just trying to win favor with those who already love me and want your money. 

Now, listen to this community-organizing, cash-for-clunkering, you-didn't-build-that, redistributionist, class-envy-agitating, crony-capitalist, Keynesian-bullshitting, economically ignorant resident of 1600 Pennsylvania Avenue. 

If those layoffs had not happened, if public sector employees grew like they did in the past two recessions, the unemployment rate would be 6.5 instead of 7.5. Our economy would be much better off, and the deficit would still be going down because we would be getting more tax revenue......

Instead of using a scalpel to get rid of programs we don’t need and keep vital investments that we do, the same group has kept in place this meat cleaver called the sequester that is just slashing all kinds of investments in education and research and our military. Yet all the things that are needed to make this country a magnet for good middle class jobs, those things are being cut. These moves don’t just hurt our economy in the long term. They hurt our middle class right now.....

Over the past four years, another 700,000 workers at the federal, state and local levels of government lost their jobs. These are cops and firefighters. About half of them are people that work in our schools. Those are real jobs. It doesn’t help a company like Amazon when a teacher, cop or a firefighter loses their job. They don’t have money to place an order. That’s hundreds of thousands of customers who have less money to spend.

See, he thinks your spending isn't good enough.  If you've got your money in a bank, it's getting spent.  He wants to put the gun to your head and spend it HIS way. 
It really is that simple.