In the 6th century A.D., Emperor Justinian codified Roman laws so that the sea and the shores of the sea, (below HW mark) must be held in trust for the use of the public. That idea passed into English common law, and then to the United States. There’s little doubt that private armororing by adding sea walls to protect private property causes passive erosion. When waves meet an unmoving barrier, they find their way around the barriers to erode the beach next door. This means the beach goes and its use is gone.