Zobel said:
It begs the question - if the government can spend money on infrastructure at will, with no penalty and obtain economic growth without end why would you ever stop? The simple answer is because you can't, any more than increasing the minimum wage indefinitely create economic growth. China is a great example of this kind of folly.
I mean, you do have to use some common sense. Don't build a bridge to nowhere, obviously, but that is just a strawman.
If you save commuters 20 minutes a day each way to get from point A to high commerce areas, point A is going to develop quickly, the real estate becomes more valuable, local public and private services spring up around point A, and the economy grows, even ignoring any Keynesian multiplier. When government spending starts to crowd out private investment, you have a problem. When government spending is on infrastructure that will increase commerce and economic efficiency on projects that private companies are not likely to spend money on, you actually help the GDP long term, and project payback can be exponential.
If you hand out checks to poor people, you only get the Keynesian multiplier.