>Worth stating is that these companies are also a significant source of unwanted volatility.
Unwanted for people holding S&P over a short timeframe, maybe, but volatility is absolutely necessary for a healthy economy. Volatility in the market represents uncertainty, and new business models and technologies bring uncertainty. A market with continuous low volatility is a market in which everything is very predictable, and hence no big innovations are happening (because it's always hard to predict how/whether big innovations will work out, so such things entail volatility).
Unwanted for people holding S&P over a short timeframe, maybe, but volatility is absolutely necessary for a healthy economy. Volatility in the market represents uncertainty, and new business models and technologies bring uncertainty. A market with continuous low volatility is a market in which everything is very predictable, and hence no big innovations are happening (because it's always hard to predict how/whether big innovations will work out, so such things entail volatility).