Note this quote:
An organizer of the rally reportedly called upon everyone to come to protest “against Marine and against Macron.” “Whatever the outcome, we will not recognize the [the results]!” he shouted via the microphone.
The Communist revolutionary way. Don't accept the results of a Democracy if your side loses.
On the other hand, French students all protest something while college age. It is a right of passage. This burning cars is not. Hope they throw they in jail for a week to think thinks over.