Dean Baker has a great article in the Guardian this morning under the above title.
As he concludes:
[W]e don't have a coherent story as to how reducing the budget deficit will boost growth – just as the creationists don't have a coherent explanation for what we know about the plant and animal kingdoms. The big difference is that the deficit hawks are determining economic policy.
That's about it, in a nutshell.
And the comparison with the creationists is a vey good one.