ILE DU LEVANT, France—On a blustery morning on this Mediterranean island, dozens of naked men and women marched arm-in-arm in defense of their right to bare bottoms.

The target of their protest was Jean-Yves Gacon, who is wielding his authority as head of the island’s homeowners association to force people to wear clothing. The coverup has the backing of the mayor’s office as well as local police who are stopping anyone who dares stroll through the village square without clothes.

...