What is the Carmagnole, and why does Lucie think it is terrible?

Caemangnole is a revolutionary song and dance that terrifies Lucie,

There could not be fewer than five hundred people, and they were dancing like five thousand demons. There was no other music than their own singing. They danced to the popular Revolution song, keeping a ferocious time that was like a gnashing of teeth in unison.

Lucie describes the Carmagnole dance as “a cruel, bad sight”