That advice is about the same as throwing your money away in the casinos and slots. It is not "investing" it is hoping for blindman's luck -- and taxing Providence to do so.
Investing in either "Index funds" or "broadly diversified portfolios" means you personally have added no value, no benefit to the rest of us. And you do do encourage the exploiter, the fraud, the schemer, the con man, the cheat and the sly thief -- because dang it all -- they know to go were the easy money is, were the marks and suckers are.
Your post shows a lack of knowledge of what index funds are. If you invest in a fund based on the S&P index, and the S&P goes up, you make money, if it goes down, you lose money. But the fund simply invests in all the stocks of the S&P, so you are buying those stocks. The fees and commissions are often lower for this type of investment and all that is required is to get in and out of the market at the right times. (Or hold the investment long term and hope for the average of around 10%). Either way, you do add value to the market by buying and holding the shares of the companies represented by the S&P.
As far as con men, or sharks, these are people who hope you give your money to them to invest, this can be risky if the manager you give your money to is not all that good, what is just what the article is saying.