I agree some, and disagree more. There also many Americans with multiple connections to other groups. Separating out the non-separatists would be another very large group.
The 30 to 40% separatists are not that strong of a group. They block and stall, but can't lead or govern. That said, if you add back in the go-along-to-get-alongs from that 30-40%, you are back at least to under 30%, maybe down to just 15% in America. We are giving a lot up to those 15%-ters, including massively disruptive change, etc. Additionally, putting out all their truly sovereign state cross border fights and fires would be orders of magnitude harder, very taxing, and extensively multitasking.
Would it not be better, simpler, and cheaper to chloroform that 15%? While I am half kidding, the real problem is our inability to rethink the structure of democracy beyond the 18th or maybe 19th century version we have. I recommend a 21st century version of direct democracy guided by an ideals algorithm.
We could start out with a shadow structure that does not require changes in the current system. That structure would be a countervailing force to the billionaire-and-corporation bought state legilatures and Congress.
Been working on the idea for a number years. Written about it on Medium, in almost every essay to some extent, or alluded it.