Keynes is as discredited as Malthus or Marx. His ideas don't even work on paper when you do the full analysis, and they've been tried several times and failed each time.
As for Friedman - in the early 1980s, Friedman's ideas in 3 years undid the problems that Keynes' ideas took decades to produce.
Someone needs to explain to Zaza that tax cuts are completely different from government spending. Tax cuts enable the economy to reinvest its own earnings. That is quite different from trying to artificially pump the economy through monetary means (which is what deficit spending means - now that it's a global economy, a global credit market, any government deficit spending isn't "borrowing abroad" but rather expanding the money supply - it's Weimar Dollars all over again, which is why gold prices have increased 2.5 times since Bush's first term).
And someone needs to explain to Michelob that Nixon continued to employ Keynesian policies - he even stated, famously, "we're all Keynesians here." Heck, he's the one who took us off the gold standard! Ford and Carter also continued to employ Keynesian policies even as the economy unraveled because of them.
The economic policy paradigm shifted with the election of Reagan in 1980. Abandoning price controls ended shortages; slowing the growth of money ended inflation; cutting marginal tax rates allowed the economy to grow "naturally" - through reinvestment of its own earnings - and federal tax revenue actually went UP in the long run.
As other countries followed suit, particularly after the end of the Cold War (thanks again to Ronald Reagan), global savings increased at a rapid pace. Foreign governments and individuals took those savings and bought US Treasurys. Greenspan, citing the risk of "deflation," took advantage of the "global savings glut" and kept interest rates too low in the mid-1990s through 1999. An economist named Ben Bernanke wrote articles about the "global savings glut" and he agreed with Greenspan's policy. This policy fueled the NASDAQ bubble - and it was completely unnecessary. After the dot.com bubble burst, rates were cut again - and again after 9/11. This fueled the housing and commodities bubbles, which were popped when the Fed raised rates starting in 2004.
Ironically, Greenspan, who had cut his teeth with the Objectivists and Austrian School economists, had become a Keynesian in practice, simply because he thought that the rules no longer applied.
But they always apply.
Austrian School. Look into it. They predicted all of this, including gold prices.
EDIT - I'm really not sure why there are 4 thumbs down votes on this answer - - I'm shocked that 50% of posters voting on this answer actually think Keynes is viable. That's a reflection on the lack of economic education in the US.
EDIT 2: the problem clearly wasn't "deregulation" - the problem wasn't just that bad deals were made. It was that the supply of credit was expanded to the point that bad deals weren't prohibitively priced. If the supply of credit hadn't been expanded beyond reason, then for the bad deals to be made, the good deals wouldn't have been made. But the good deals AND the bad deals were made. Subprime mortgages DIDN'T CROWD OUT prime mortgages. Jumbo mortgages DIDN'T CROWD OUT conforming mortgages. With a finite and stable supply of credit, there is a risk/return frontier - the risker the deal, the higher it is priced - the higher pricing limits the number of risky deals that can be done, because they don't cash flow even at the start. When you artificially reduce the cost of credit (by increasing its supply), a lot more bad deals cash flow, at least at the initial rates. This has an overflow effect as people and businesses take that credit and spend, creating income for someone else.
Look at it this way - say you have a 25,000 gallon swimming pool. You dump 28,000 gallons in. 3,000 gallons flood out. They may flood out only on one side - but the problem ISN'T that there isn't a levee or other barrier on that side, the problem is that there are 3,000 gallons too many.
Keynes himself was brilliant of course - just like Greenspan, he retained his influence, power and paycheck by telling those in government what they wanted to hear - i.e., that they could "engineer" a successful economy.