The obvious question is will the US government allow one of its most profitable states to leave? Highly doubtful. Great way to start another civil war, though!
Personally, I am ambivalent (and technically I am a Californian).
Good grief.
The lunacy is bipartisan.
So, you support states rights? Tell me why abortion is a federal issue then?
Sanctuary cities don't change anything about international borders or who can enter the country, because international borders are federal issues with federal staff. Sanctuary cities refuse to make their local staff spend time and money reporting on immigration status every time they issue a parking ticket. It's not even a states rights question - nobody even suggests that city officials should check if you have paid your federal taxes every time you take to them, but that's not because (normal) people are objecting to a federally run tax system.
I do, however, think sanctuary cities (which are so fuzzily defined legally...) create an incentive for illegal immigration. It sends a message that one need only get through the border to make it permanent. My family immigrated legally. They should too.
If states choose not to enforce federal law, I think they need to clearly establish a legal position as to why.
As for sanctuary cities, when your state is sitting on territory that was formerly part of Mexico, its major cities still carrying Spanish names, its labour force overwhelmingly dominated by Latinos, it doesn't seem crazy at all to question the rationale of the US immigration system and borders and try to accomodate to the realities of the actual real world demographics.
Not to mention from my understanding sanctuary cities have their origin with the migrant fallout created by the central American wars that the United States was directly involved in.
As for "overwhelmingly", you make it sound like we're living in Mexico but have the indecency of calling it the US. As for the current state of population, LA is around 50% Latino at most. That isn't illegal immigrants. Those aren't people that identify as Mexicans in America. Those are Americans. Some even voted for Trump.
All territory was formerly part of someone else's territory. Borders move and people along with them. I feel no moral burden to accommodate previous inhabitants, nor would I expect any if the table was turned. That said, if states truly moved to nullify federal law based on a tenable legal position, I'd listen. However, they'd have to make such an argument, as opposed to a philosophical one (like yours, which I don't agree with).
As for your "understanding" of the origin of sanctuary cities, you've been reading fake news.
In our two party system, the lesser parties normally never get included in the legislative process. (those primaries effectively exclude them) In a parliamentary system any party that gets enough votes will get some seats.
If we adopted that sort of system you'd immediately see some greens and libertarians involved in the legislative process, and presumably you'd see an end to jokey pseudolibertarians in the Republican party, since everyone would just vote for the real thing. The "you're just throwing your vote away" disincentive would no longer exist. (based purely on how often that topic comes up in conversation during elections, I assume you'd see some big changes in the ideological makeup of the legislature)
I hate the Alt Right and the Ctrl Left pretty equally.
True, the Democratic Party is basically a coalition where the two main factions are the dominant center-right neoliberal faction (the "Third Way" that reached its peak under Bill Clinton and his since lost some ground in the party while still remaining dominant, if barely so) and the secondary center-left progressive faction.
The Federal government has to enforce its own laws. The States may voluntarily assist, but the Federal government has no authority to mandate that states, or subdivisions thereof, enforce federal laws.
Indeed, Roe v. Wade or Gay marriage too. I mean, my state voted in gay marriage willingly, but I imagine some more religious states may want to determine the laws in their own state, like California does with weed and immigration
Also, not allowing abortions desperately increases the tax burden.
You get the entire Los Angeles basin. You get most of the Bay Area: the area served by BART, Berkeley, things west of Berkeley, and Marin County. You also get everything in the middle. Generally the border runs along the ridge of the coastal mountains.
The USA keeps San Diego, Eureka, Davis, Fresno, etc.
You get exclusive rights to the "California" name. The USA will split the leftover bits into at least 3 states.