The majority of Californians believe in rights that will be taken away under the new government leaders. Same sex marriage, a woman's right to abortions, and net neutrality just being a few of those rights.
Allowing California to secede will help prevent mass revolution when these rights are taken away. California's economy should be able to help sustain the state as its own country.
Puerto Rico can become a state so the US flag won't need to be changed.