I am not "anti-indexing", but I think that most investors have not realised the impact that indexing has had on the world of equity investing, how it has fundamentally changed the nature of investing, and the implications of this going forward.
The universal law of investing is that in order to make excess return you must take risk. The risk is that whatever you buy today could fall in price and you are holding an (unrealised) loss. Its generally accepted that equities provide the highest return over time because companies are the wealth-creating engine of a market-based economy. Over time this has borne out to be true; stocks have outperformed every other asset class over the 200-years or so since the industrial revolution.
However, prior to 1974 there was no such thing as an index fund. Buying equities meant you bought shares in companies directly. That meant your investment could go to zero if the company failed (and they often did, of course). This is the very real risk that active stock pickers today still bear.
Indexers rightly point out that while individual companies can go bust, the stock market itself will never fall to zero. This risk has been removed. They also rightly point out that indexing allows you beat the majority of active funds over longer holding periods. Better returns.
So Indexing gives you less risk, better returns.. what's not to like?
Except this now violates the first axiom of investing; that better return generally requires one to take on more risk.
The problem now is that if indexing has made equity investing safer, more predictable, cheaper, and more accessible for everyone, then... why should it reward them just as well as it has done for previous generations who bore much more risk? Market theory says that.. well, it shouldn't, and the risk premium of holding stocks, or at least index funds, should be greatly blunted.
Translated, what I am saying is if equity investing is are less dangerous than in the past, then to compensate for lower risk you should expect lower returns than the asset class has historically delivered. Maybe that is what we are seeing in this cycle as markets adjust to seemingly ever higher valuations over prolonged periods.