Emerging market stocks and currencies tumbled in late 2013-14 amid the "taper tantrum" that resulted from the Federal Reserve cutting its bond purchases.

Now there's talk that emerging markets are vulnerable again. The thinking goes: "U.S. interest rates rising? Sell emerging markets," writes Wall Street Journal Heard on the Street Columnist Richard Barley.

"Eurozone standoff with Greece? Sell emerging markets. Problem in a couple of emerging-market countries? Really sell emerging markets."

But that represents "outdated thinking," he argues. "The story since the global financial crisis broke out has been one of belated realization that risks in developed markets have been underpriced." Barley cites U.S. mortgage-backed securities and eurozone government bonds as examples.

Meanwhile, emerging market economies are growing faster as a whole than their developed counterparts. "The bigger puzzle surely is the lackluster growth in developed economies given the sheer scale of stimulus thrown at them since the crisis," Barley states.

When it comes to stocks, the MSCI Emerging Markets index has risen 6.3 percent so far this year, compared to 6.1 percent for the MSCI Developed World index.

Stanford University economist Michael Boskin, former chairman of President George H.W. Bush's Council of Economic Advisers, offers a more pessimistic view.

Things aren't looking so hot in the economies of Brazil, Russia, India, China and South Africa (BRICS, which helped fuel global economic expansion and financial market rallies in recent years, he writes on Project Syndicate.

"A few years ago, pundits and policymakers were predicting that the BRICS would be the new engines of global growth. Naive extrapolation of rapid growth led many people to imagine an ever-brighter future for these economies--and, thanks to them, for the rest of the world as well," Boskin says.

"But now the bloom is off the rose. The economies of Brazil and Russia are contracting, while those of China and South Africa have slowed substantially. Only India’s growth rate has stayed up, now slightly exceeding China’s." Chinese GDP grew 7.4 percent last year, the slowest rate in 24 years.

And the BRICS' trouble may continue, Boskin says.

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