Even assuming that's true, one can't say the sort of risk and investor took on 15 year look-backs since WWII has been evenly distributed to get some sort of acceptable return, nor can one say that this will continue hold true for the next 15 years. You may believe it hold true though, and many do… but very few will do their homework on the risks to their "diversification" and their own changing liquidity constraints that will occur over the "sufficiently long time-horizon"

I didn't say I didn't believe in investing, just that I don't consider it any different from speculating, just the time frame typically involved.