Saying "you can't secede" ignores reality where localities can, and do, declare independence. It can happen regardless of what "official" mechanism exists. So what I'm hearing is, California just flat out says they're seceding and dares the US to stop it.
Okay, granted. However there’s the practicals to consider, like interstate commerce, military bases, out of state workers and vacationers, energy and water infrastructure, etc..
Given the alternative is being a controlled and occupied territory of the 4th Reich, I'll take the secession option and it's complications.