Land is private property. Navigable water is open to the public. The strip of beach itself is the issue. If people have their feet in the water (or are below an accepted well-defined high water mark) and are traversing the beach (no lingering or stopping, no dogs, no nada) = no problem.
Any other activity is trespassing, just as if someone came into a fenced yard and had a picnic, or urinated or defecated, or left trash, etc.
If I owned beachfront, having paid a high price and high taxes for it, I would not be willing to let strangers do anything but legal traverse described above. If you want to picnic or swim or linger, go to a public park or buy a beachfront lot.
The primary right of private land ownership is the right to privacy, the right to exclude others. If it’s not yours, why not just stay away.
