Just to be clear, this isn't cherry-picked data where I only included the boom periods. No, this is the whole enchilada -- good periods, bad periods, indifferent periods.
People have been screeching bubble bubble bubble non-stop for centuries. When the stock market dares go up, "it's a bubble". When it goes down, "See I told you so". That's what makes them the smartest people in the room. Heads I win, tails you lose. So while they always win the rhetorical wars with this unbeatable formula, I prefer being stupid and having money instead.

Over the past 20 years, it has grown 6.3710 fold, an average annual increase of 9.7%/year
Over the past 50 years, it has grown 131 fold, an average annual increase of 10.2%/year
and so on.
This is from the below link, which also has similar for bonds, Treasury bills, and gold. These don't come close to matching the increase in equities.
http://pages.stern.nyu.edu/~adamodar/New_Home_Page/datafile/histretSP.html
Simulation after simulation by countless authors and organizations show one is more likely to exhaust their nest egg if it is all in fixed income like bonds and CDs than if it is majority equity. Nothing holds up as well in the face of withdrawals and inflation than does equities, except perhaps real estate. In other words, it's an even bigger gamble to not have a sizable proportion in equities.
That said, being an old person, I hedge by having about 40% of my easily re-investible assets in bonds and other fixed income. On top of that, I have an annuity, Social Security income, my house -- all non-equity investments or sources of income. So I'm far from being an "all equities" fanatic.