The main argument (passive investing) has issues when inflation is high, pulling this from a newsletter I read recently:
"Bianco further notes that, for an investor who bought the S&P 500 in 1966, it would not have been until 1993 — 27 years later — that the holding would have delivered real, inflation-adjusted gains."
Real inflation adjusted gains are one thing, protection against inflation is another. Stocks deliver both, though with significant risk. But if you are passively investing, the inflation protection you get is essentially free.
You will still have to fade the risk though. If your portfolio is large and consists of 100% stocks, you need to diversify out. The mostly common alternative asset classes are real estate, commodities, and cash.
"Bianco further notes that, for an investor who bought the S&P 500 in 1966, it would not have been until 1993 — 27 years later — that the holding would have delivered real, inflation-adjusted gains."