Are investors hurting themselves with ETFs?

While ETFs have been around for nearly 25 years, they have really exploded in the past five. Exploded in terms of the assets invested in these half-stock, half-fund hybrids (more than $2.5 trillion among just U.S.-listed ETFs as of December 31, 2016, according to FactSet), the sheer number of products (nearly 2,000 listed on U.S. exchanges), and the trading volume on major markets (about 30% of daily volume in the United States during 2016, according to Credit Suisse).