Many modern economists think the standard for a "good" economic theory is how well it predicts future trends. Not only are most economists terrible at making predictions, but the whole premise of economics as being about predicting things is a flawed idea.
Loose monetary policy can get people to use idle resources. But this new economic activity will likely be in the service of bubble industries that don't create real wealth. Moreover, these bubbles create many idle resources of their own when the bust comes.