BlackRock said in a position paper last week that bond exchange-traded funds helped “defuse uncertainty and facilitate orderly and stable markets” while billions of dollars poured out of Pacific Investment Management Co. in recent weeks.

BlackRock's paper, which isn't attributed to any specific authors, examined heavy trading in two broad-market bond ETFs, the iShares Core US Aggregate Bond ETF and the Vanguard Total Bond Market ETF, since Bill Gross's departure from Pimco on Sept. 26.