I'm reading this differently, but I'm also not an attorney. The FAA regulates your behavior in the air, including 0-500'. And Congress has established airspace above 500' as public right of way. But teh space below 500' is the exclusive domain of the land owner. From the Wiki article "...but the Supreme Court rulings and space treaties are clear. A landowner's domain extends up to at least 365 feet above the ground. see
Causby v US (1946)" That Supreme Court decision established that flight operation in that lower window is considered a "taking", just like seizing your property for a new highway.
And it doesn't matter how old the decision is. It still stands.
Now there is a clear distinction between operating over private land vs over land where you already have a right of access. For example, the ocean and most inland water bodies are public access, so that extends to the low flight zone over it. The same would be true for other public lands, or lands with public right of way. So you could fly over public roads, but not over the adjacent property that its private.
It really distills down pretty simply. If you have right of access to the land, you have similar right of access to the low flight space over that land. If you do not have right of access to land, then you also don't have right of access to the low air space over it. To fly over private land, you need to go over 500' (365' in rural areas).
Also, don't confuse lands that are open to you, with lands where you have a right of access. The two things are very different. Lands open to you are still full controlled by the landowner, and they can revoke permission at any time, and can similarly decide if they want to extend access to the airspace that they control. So don't assume that if you have access to the land, you also have access to the airspace. A right of access means that you have a right to access or cross the land, and nobody can deny you access. That's very different from being voluntarily invited to use land.
Using the example of a drone circling your boat in an anchorage, that's no different than someone circling your boat in a kayak. The waters are public and anyone can go anywhere they want, within limits of regulations. But someone circling your house is another thing all together, assuming you own the surrounding land where the drone is operating.