The presiding argument for investing in index funds and passive exchange- traded funds is simple: They tend to cost less and perform better than their active counterparts.

Certainly, in broad categories like large-cap domestic equities, it can be hard to make a case for active management: Only 12 percent of active U.S. large-cap growth funds, for example, beat passive peers over the last decade, according to Morningstar's latest Active-Passive barometer.