French President Emmanuel Macron’s standoff with striking railway workers is a major test of his economic reform campaign, comparable to Margaret Thatcher’s stare-down of the British coal miners union two generations ago. So it’s significant that the Frenchman is winning the battle for public opinion.

The latest French Institute of Public Opinion poll released over the weekend by Le Journal du Dimanche shows 58% of respondents think national operator SNCF’s strikes are “completely” or “rather” unjustified. Nearly two-thirds...