"Mainstream economics" to the real scientific economics is like astrology to astronomy.
If you are interested in real understanding of economics, read Hayek, Mises, Rothbard, forget Keynes and Krugman.
"The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design." -- Friedrich von Hayek.
The only reason Keynesian "economics" views are so popular is that such "economists" provide "scientific" backing for politicians' plunder and manipulation of people.