Investors are asking the wrong question about the Bank of Japan. It's not whether Haruhiko Kuroda will ease further this year (he will), but will it do any good?

There are many reasons for Gov. Kuroda to act, perhaps as soon as Friday: persistent deflation, negligible global growth, jittery stock investors, antsy politicians who need placating. Here's why he shouldn't: Japan's weak-yen experiment is backfiring.

This contrarian take on the Bank of Japan's two-day meeting that began on Thursday would seem to ignore the good that's come from the yen's 30 percent drop since 2012. That includes record corporate profits, a tourism boom and, until recently, a buoyant stock market. But these benefits aren't enriching a broad spectrum of Japanese. Companies aren't sharing the spoils with workers, while inflation expectations remain, in Kuroda's words, "somewhat weak."