US index funds face rising risks from mega-cap concentration and passive investing trends.

US market index funds, especially cap-weighted ones like the S&P 500 and NASDAQ Composite, are increasingly dominated by a few mega-cap stocks, reducing diversification and raising structural risks. The upcoming IPOs of SpaceX and OpenAI may worsen this concentration, increasing risk exposure for investors. Given these trends and challenges in the tech sector, investors seeking diversification should consider options beyond US index funds. The article advises skepticism and caution amid speculative market behavior.