The USA currently spends billions on the military. If some of this was redirected to the Space Program the USA could reap enormous economic rewards and also make advancements in nearly every scientific field.
The establishment of a Lunar Colony will create and entirely new incentive for innovation, education, job training and nearly any associated field. This is the sort of project America needs to demonstrate our power and ability in a non-violent way.
We can afford it. It will make history. It will benefit us economically.
I can't think of any better reasons to invest in something.