Chris, you need to understand that government can't "invest."  The best they can do is take from the industrious and give subsidies to those who are not, and to projects that are financially unsustainable without subsidies.  

If government left that portion of tax money in the pockets of those who earned it, those people would invest it.  Or maybe they would spend it.  But either way, the economy would do better with direct spending/investment by those who earned it, rather than sending the money to Ottawa and hoping to get a trickle back after postage and handling.