[avar]

I think you're arguing a point that isn't even being brought up in this thread or in the article.

Of course it's just fine to have an index fund that's weighted towards certain types of stock, e.g. there's the S&P 500, then various "woldwide" funds, EU-weighted funds etc. The risks & benefits of those are well understood. Nobody argues that different types of index funds shouldn't exist.

Similarly, there's funds that cater to specific regulations, e.g. investing heavily in "green" stocks which may be subsidized by the government, or avoiding certain taxes (e.g. lower turnover for lower capital gains).

Both of those are categorically different from supposing that you know better than other people that tech stock in 2017 is overvalued, and trying to move away from that in favor of something else. Now you're making an active investment move which history shows you're more likely to lose on as gain anything on.