From the article:

“This is absolutely not the right time, from both a macroeconomic and a political standpoint,” to discuss canceling public debt, said Lalucq, an economist by training, who highlighted the same criticism many of her peers have raised.

While she, along with leading economists, advocated for such a measure at the end of the Covid crisis, circumstances have radically changed, she said. Inflation is now a key concern, and such a measure would worsen the problem.

I don't know anything about the topic, or what France's interest payments are like, but the topic isn't as out there as it implies. Many of the people critical of it were just in favor of it a few years ago. I also have no idea how serious the candidate is about this. Is it just something they mentioned off the cuff sometime? Also, as far as I'm aware, this is not really a leftist position. This is the position of one particular candidate. This seems to be the main point; it's to get people discussing it:

For Mélenchon and his allies, whether or not his proposal flies is perhaps not the main issue. He has succeeded in putting fiscal orthodoxy itself up for debate.

"We are very happy there is a controversy on debt," said Antoine Léaument, a member of France's National Assembly with France Unbowed, on the sidelines of the rally.

"Debt is the excuse used to roll back social rights,” he added. "We'll take whatever comes our way. We're game."

btw you don’t need to write a narrative for yourself about what you perceive me to be, you can get off your high horse and just ask

It was a narrative about perception of yourself. If you think you're too smart to be wrong then you're probably wrong. The only possible way to be right continuously is to enter everything with an open mind, and a willingness to change when proven wrong. Assuming everyone not agreeing with you is an idiot is only going to ensure you can't understand what they're discussing.