There is no place and no time for "supply-side economics." "Supply-side economics" is not a legitimate school of economic thought. It was concocted by a political scientist named Jude Wanniski, not an economist. Very few economists have signed onto this garbage and the ones who have are generally considered to be flakes.
The crowding out of capital argument is of dubious merit and it is inapposite when we are at the zero bound with interest rates, where savings exceed investment.
Paul Krugman has a good blog today:
http://krugman.blogs.nytimes.com/2011/07...alvinball/
I could go on and on with this but you would only glaze over. Sorry.