Why do recessions happen? To clear out the bad investments accumulated during a boom. The economy cannot truly recover until those investments are cleaned out of the system. Government efforts to cut the liquidation short will prove to extend the duration of the process, not make it shorter. "Stimulus" is designed to prop up bad investments in the hope that the market will find a way to recover without letting the worst offenders fail. "Stimulus" money has to come from somewhere. Government redirects capital from productive uses into politically determined allocations. Government projects are easily seen, what is unseen is what would have been done with that productive capital had the government not directed it to political purposes.
Henry Hazlitt expounded on the seen vs unseen in Economics in One Lesson. Here is an excerpt from his chapter. He uses a bridge as an example:
"Two arguments are put forward for the bridge, one of which is mainly heard before it is built, the other of which is mainly heard after it has been completed. The first argument is that it will provide employment. It will provide, say, 500 jobs for a year. The implication is that these are jobs that would not otherwise have come into existence.
This is what is immediately seen. But if we have trained ourselves to look beyond immediate to secondary consequences, and beyond those who are directly benefited by a government project to others who are indirectly affected, a different picture presents itself. It is true that a particular group of bridgeworkers may receive more employment than otherwise. But the bridge has to be paid for out of taxes. For every dollar that is spent on the bridge a dollar will be taken away from taxpayers. If the bridge costs $10 million the taxpayers will lose $10 million. They will have that much taken away from them which they would otherwise have spent on the things they needed most.
Therefore, for every public job created by the bridge project a private job has been destroyed somewhere else. We can see the men employed on the bridge. We can watch them at work. The employment argument of the government spenders becomes vivid, and probably for most people convincing. But there are other things that we do not see, because, alas, they have never been permitted to come into existence. They are the jobs destroyed by the $10 million taken from the taxpayers. All that has happened, at best, is that there has been a diversion of jobs because of the project. More bridge builders; fewer automobile workers, television technicians, clothing workers, farmers.
But then we come to the second argument. The bridge exists. It is, let us suppose, a beautiful and not an ugly bridge. It has come into being through the magic of government spending. Where would it have been if the obstructionists and the reactionaries had had their way? There would have been no bridge. The country would have been just that much poorer. Here again the government spenders have the better of the argument with all those who cannot see beyond the immediate range of their physical eyes. They can see the bridge. But if they have taught themselves to look for indirect as well as direct consequences they can once more see in the eye of imagination the possibilities that have never been allowed to come into existence. They can see the unbuilt homes, the unmade cars and washing machines, the unmade dresses and coats, perhaps the ungrown and unsold foodstuffs. To see these uncreated things requires a kind of imagination that not many people have. We can think of these nonexistent objects once, perhaps, but we cannot keep them before our minds as we can the bridge that we pass every working day. What has happened is merely that one thing has been created instead of others."
I've focused on the "against" side. The "for" side is readily available in the writings of Paul Krugman and others.