Meh. Not really. In parliamentary systems, you might have a lot of parties in the mix, but they caucus and forms blocs. Same happens here, just upstream through primaries. Democrats have centrists and progressives and a fringe of anarcho-socialists. Republicans Ave moderates, conservatives, libertarians, Tea Party, and whatever the Alt Right is.
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.