If you're invested in an index fund, wouldn't the only way to realize the loss during a recession be to sell? Anyone who stayed the course after 2008 would have seen record gains in the years following.
Or buy annuities, setup a bond ladder, or hold dividend stocks, but these have their own, related issues.
Early in the accumulation phase, however, I completely agree with you -- you're making the central argument for a long-term buy-and-hold strategy.