I don't disagree with you, but I will add (yes, I'm having a Captain obvious moment) that focusing solely on PE ratios can be misleading because earnings vary so much. The PE for the S&P 500 was 70.91 on 1/1/09, and the S&P was 865.58. Yesterday the S&P was 3,374.85. After adjusting for inflation the gains are not quite as impressive, but still good.
Inflation Adjusted S&P 500 chart, historic, and current data. Current Inflation Adjusted S&P 500 is 5,726.02, a change of +24.84 from previous market close.
www.multpl.com
I have yet to figure out a way to accurately predict earnings. Here's one prediction:
I have no idea if this is accurate.
Index funds have done well for me over the years, but this might be a bit of a historical anomaly. For example, with reference to the inflation adjusted S&P 500, a person who steadily bought stocks between around 1955-1975 would not have broken even until roughly 1990. A person who bought a basket of S&P stocks in 1910 would not have broken even until around 1955. Conceivably, A person could have bought stocks in 1910 and sold in the early 1980s and just broke even.
One can of course pick different starting and ending points that will give very different results. My only point is that it is entirely possible to buy and hold over a relatively long period of time and end up basically breaking even.
The possibility that there will be a long (relatively) flat stretch of 20-30 years bothers me more than the possible sharp drops. Sharp drops tend to be followed by sharp rises, but a long flat market will cook me and my index fund investments like the proverbial frog in a slowly heated pot of water.