In the view of many economists at the International Monetary Fund and, say, Emmanuel Macron, a former economy minister of France and now a presidential candidate, the fundamental cause of unemployment in France is a rigid labor market — not, as Mr. Mélenchon and others argue, inadequate demand in the economy. So their proposed fix is to lower labor costs by reducing the bargaining power of unions, making it easier for employers to dismiss workers and raising eligibility requirements for social or unemployment benefits.

Reforms of this kind have been passed over the last few years, including the so-called “loi Macron,” which relaxed rules for letting employees go. More have been recommended by the I.M.F. and European Union authorities.

But — to take just one example — cuts to France’s pension system in 2010 were as unnecessary as they were unpopular. The year before, projections by the European Commission showed that spending on public pensions in France would increase by just 1 percent of G.D.P. over the next 60 years. Given that France’s G.D.P. was projected to more than double over that period, that increase would have been eminently affordable.

So why not put some money into public investment that will provide positive real returns while creating new jobs?

Yes, high unemployment has been a fixture of the French economy for several decades now. But a major fiscal stimulus could spur overall demand in the economy, and that would encourage employers to hire workers.

The French can also afford their cherished welfare state because labor productivity in France is high — just above that in Germany. A better output per hour of labor allows for decent wages and, with sufficient taxes on both labor and capital income, for social expenditures that provide some measure of economic security.