The real story here is that the sums involved are ludicrously trivial; eliminating everything on Cantors list would amount to a rounding error on federal spending.
The truth is that it has always been like this. Ever since Reagan, the conservative approach has been to talk about the need for smaller government, but refuse to offer any serious proposals for spending cuts, pretending instead that there are large sums being wasted on things nobody wants.
Krugman is right of course. This is about grandstanding not solutions. The GOP is simply not interested in any real cuts in spending. They just want to blast the Dems.