It's much more difficult to justify making someone redundant (licenciement économique) or to fire someone who has become an asshole or isn't performing. In other jurisdictions where I've worked, the employee gets their notice period. In France, the employer is often under implicit threat of an inspecteur du travail, a government work inspector, who will wrap the company up in shitload of bureaucratic audits.

The likelihood of an employer firing people abusively is much greater than an employee being an asshole.

It can indeed hinder start-ups a little because of uncertainty in any new ventures.

But keep in mind that the vast majority of workers are not working in a startup environment. Relaxing a law to fit the legitimate needs of a small number of start-ups with an even smaller proportion of the work force at the detriments of the vast majority doesn't seem like a good idea.

And I've seen people getting fired when redundant and/or toxic for the company. The administration will keep an eye on you if you fire more than a dozen employees per year (for a 1500 employees company), when firing "en masse" (ironically named "plan de sauvegarde de l'emploie") an employers has some obligations like giving opportunities for training, maybe finding another position in the firm, firing people close to retirement with some compensation until their actual retirement (pre-retraite).

Lastly, this protection goes both ways, if you, as an employee, you end-over your resignation, you must remain in the company for 3 months, that way the employer has time to find a replacement and schedule a knowledge transfer in good conditions.

>>The likelihood of an employer firing people abusively is much greater than an employee being an asshole.<<

Not my experience in the jurisdictions where I've worked, but certainly a widespread belief among many French people.

>>Relaxing a law to fit the legitimate needs of a small number of start-ups..<<

I think the French labour laws need to be relaxed for the good of the French economy, not just for start-ups. The current system benefits those already in employment by entrenching their positions, but to the detriment of younger people seeking work.

The employee knows about probationary periods and adjusts his behavior to them.

People can, and do, change.