President Barack Obama has consistently insisted that the wealthy should pay their “fair share” of taxes. Sounds fair enough — assuming that you can trust the Internal Revenue Service to play fair.

But how much of a person’s income — or a company’s profits — is government’s “fair share”? And how high can taxes go before they become not just unfair but unproductive in generating government revenue?

That defining debate persists. However, there should be no debate about the folly of elevating taxes on the rich to this ludicrous level, as reported last week by Reuters:

“More than 8,000 French households’ tax bills topped 100 percent of their income last year, the business newspaper Les Echos reported on Saturday, citing Finance Ministry data.”

The over-the-top taxing included a 75 percent surcharge on incomes of over one million euros, fulfilling a 2012 campaign pledge from Socialist Francois Hollande in his successful run for president.

Fortunately, though, France’s Constitutional Council, which more or less serves as the nation’s highest court, has rightly ruled the truly confiscatory tax rates on the well-to-do to be “unfair.”

The Socialists now plan to inflict that extra bite on companies instead of individuals — another sure formula for further stifling France’s long-struggling economy.

At least some Americans who favor hiking taxes on the rich in our country recognize that President Hollande has stretched that concept beyond the bounds of reason.

For instance, George Washington University Law School Professor Jonathan Turley is a well-known commentator and author — and a self-proclaimed advocate of a “socially liberal agenda.”

Yet citing what friends in France have told him, Prof. Turley wrote this week on his blog:

“The government is getting instant revenue while killing revenue-producing businesses. It is like eating the grapes and roots of the vineyards of Bordeaux for food and leaving the fields barren.”

And: “Hollande’s expressed hatred of the rich resulted in a political success and now an economic disaster.”

So when deciding what a “fair share” of taxes should be, recall the ill-advised slaughter of the title character in Aesop’s “The Goose that Laid the Golden Eggs.”

And heed France’s modern confirmation of that ancient lesson.