I'm taking your "we've solved the business cycle!" comment as my sell signal. Everything is rosy until it isn't. I have a very opposite, pessimistic view, that this great fear of even the slightest downtown means we're just putting off the day of reckoning until it really comes crashing down.
The fact is the prosperity of the past 10 years has come with huge and growing imbalances that can't continue ad infinitum. Deficits are gigantic, and at some point all this money we've been lending will require higher interest rates for people to buy our bonds. When that happens, watch out.
During boom periods, credit conditions are loose. Which allows for a large degree of innovation with new and speculative business models. This is important because as conditions and technologies change, the frontier space of what's viable needs to be explored. Tomorrow's economic titans are today's wild-eyed entrepreneurs.
However most of these crazy ideas turn out to be just that. That's where the importance of recessions come in. Credit crunches and market downturns impose economic and efficiency disciplines. Firms that were coasting by on good conditions without delivering real productivity gains are culled by the downturn.
The entire phase of the cycle is important to maintain a healthy economic ecosystem. My fear is that if we banish recessions to the dustbin of history, we'll find ourselves increasingly burdened with bad investments as a larger and larger share of the capital base. Instead of getting written off during a downturn, jubilant markets will just keep throwing good money after bad managers, broken business models and overhyped vaporware.
On a broader view, the amount of cash that governments like US and China able to infuse in the system at moment's notice is unparalleled. The big 5 tech alone harbors cash of $0.5T and capable to weather any storms. If you think of US or China as one organism, they have achieved enough of collective wealth and enough cash just sloshing around that any new recession can be absorbed away.