I think people exaggerate how much the bubbles really achieve. The eye is drawn to the price peaks, but where are we right now?
Conventional wisdom, in hindsight, seems to suggest that 1990 was a fantastic year to buy and hold an index fund. But that's not necessarily accurate. S&P500 opened 1990 at $350, and it's $1100 now. Fourteen years, average appreciation 8.5% per year. (BTW, 10-year treasuries were paying 7.9% in early Jan 1990.) Similarly, 50% from the past six years is only 7.0% appreciation per year.
I don't know which side of the debate this puts me on, but I look at this supposedly spectacular run-up over the past ten or fifteen years and I don't see even the 10% or so that a ho-hum stock market supposedly returns.
Yeah, one coulda (one shoulda) got out at the peak. But that sure as shit wasn't the conventional wisdom at the time.
So one could look at all these crotchety nay-sayers since 1990 or earlier, and say: yeah, they were right, it's been a disappointing decade or two for stocks.