It's important to notice that any argument in favor of public access to beaches can be applied to any kind of desirable land. One could make an isomorphic argument about mountaintops: "The concept of a private mountaintop is backwards and unethical. Why should rich people be able to restrict others from hiking to the top and enjoying scenic views?" Should we ban private ownership of mountaintops?

Public beaches are a good thing, but it's wasteful to ban ownership of all 840 miles of California coastline. Some people want private beaches, even if the law doesn't allow for it. They'll lock gates, block roads, and otherwise shirk the law to get what they want. The state then must then expend significant resources discovering and sanctioning these people.

A better solution would be for the state to tax private beaches. That would collect significant revenue from people like Khosla while still allowing only a small fraction of the coast to be privately-owned.

Edit: I'm not saying we should ban public beaches. I'm saying allow something like 20 miles of private coastline and auction off the rights every year. The other 820 miles of coastline would remain public, and the state would collect millions in revenue to be used for social welfare.