Dan Loeb is taking Japan's economic renaissance at face value: the hedge fund manager wants Sony to spin off its entertainment arm. Loeb's idea may have merits. The electronics giant should take him seriously.

Compared to his sometimes caustic attacks on US corporations, Loeb's May 14 letter to Sony Chief Executive Kazuo Hirai is studiously polite. He argues that Sony's movie and music operations aren't performing as well as some peers, and would do better if publicly listed.

The merits of Loeb's plan are open to debate. Sony has long argued that movies and music help its hardware business - for example, by turning blockbusters into Playstation games - though it has struggled to quantify those benefits. Besides, Sony is not exactly a troubled stock: its share price has doubled since earlier this year.

Yet it would be a mistake to dismiss Loeb out of hand: his proposal values the entertainment businesses at more than half Sony's current market capitalization. As he has demonstrated at Yahoo and elsewhere, he is not scared of a drawn-out public fight.

The author is Peter Thal Larsen, a Reuters Breakingviews columnist.