Keynesian economics fill two vital functions in an up-and-down economy. In the "up" cycle, the government pays down the debt and limits borrowing so the private sector can do its thing.
Our Republican friends cut taxes, borrow money and funnel our grandchildren's cash to the uber-wealthy. Witness what Ronald Reagan, George H. Bush and George W. Bush did as opposed to what Bill Clinton did.
In a "down" cycle, the government borrows money and makes needed investment in our infrastructure. This increases aggregate demand and primes the pump in our economy. Our Republican friends cut taxes, borrow money and funnel our grandchildren's cash to the uber-wealthy.
The real genius is that there are things the private sector can or will not do that are vital to the progress of our country. Keynesian economics is a beautiful system that allows individuals and companies in the private sector to fly on the "up" cycle and allows us to do the necessary things that have to be done to advance and maintain a decent civilization on the "down" cycle. It worked wonders and created the biggest middle class the world has ever seen, before Ronald Reagan and "supply side economics."
Why should we not go back to what worked so well for 50 years? You have to ask your Tea Party or conservative Republican friends, for they seem to like this economy they created with their economic ideas.