Communities are fully in control how they manage themselves, as long as they do it within the law of the state.

Rancho Palos Verdes should comply with the law, or face the consequences of not being able continue that control of their land management.

A great value of democracy is that a "random activist" can petition the government to enforce the law, that's how we keep the whole thing in check. The idea that random activists could not be a check on illegal behavior of the government is a very, well, authoritarian idea that is not compatible with any of the values embodied in the US or California constitutions, our legal system, or the very character and culture of the US.

US cities are under the jurisdiction of their states. States hold the power to abolish or establish cities. Cities are required to follow state law. Whether residents or non-residents remind cities of their legal obligations is utterly irrelevant.

If a city was allowing racial discrimination and no one within the city sued, would that make it ok?

That's a euphemism for NIYBY.