If one assumes that we are in normal times than the level of the stock market is hardly alarming. While the market is not trading at bargain valuations, the multiple is roughly inline with history. Unfortunately, there are glaring imbalances and these earnings are dependent on a $1.4 trillion deficit, state deficits, 0% interest rates and money printing.
The mistake investors made in the last cycle was to ignore that earnings were a result of a real estate and credit bubble as multiples looked rational in 2007 as well. The problem with betting aggressively against this market based on this rationale is that the cash flows being generated by corporations are real even if they are not sustainable. They are using these cash flows to buy back their stock and other companies, buoying the market.
In order to bet aggressively against this market, other than for a trade, something needs to happen to disturb the cash flows of corporations or make them worth less. I believe inflation and higher interest rates have the greatest chance of doing so. We are still a finance driven economy and higher rates would be detrimental to the economy and corporate profits.
This does not mean we will not see corrections or that the market will remain a one way affair. It only means that in order to see a renewed bear market I believe something will need to happen to change the current dynamic.