Men telling women? Nothing to do with men wanting to ogle women’s bodies; don’t make this about that.
Corsica belongs to France and the former is extending the French republican view which is not to deliberately make yourself so different in attitude that you are effectively declaring separatism and apartheid.
If I were to wear a cross or star of david on the outside of my blouse, I would be signalling that I want everyone to know that I am of a faith. Why would I want passersby to know ….. for what reason? Similarly with dress that runs contrary to French life & culture, and now the burkini. As another poster said upthread, their culture and ethos are very important to French people, and they go out of their way to protect that.
What's wrong with remaining modest, being on the beach, enjoying a swim in a swimming costume as per the culture of the country you have moved to? In England there was a rucus recently about a public swimming pool being temporarily segregated for Muslim women only. This trend is not helpful for co-existence, and trashing the host culture by implication is exceptionally ill-mannered.