That is a strange argument coming from someone who a few paragraphs up said that the UK newspaper articles, asserting that Spain would veto Scottish entrance into the EU, were wrong.
There is nothing in the US constitution forbidding secession, that is also easy to check. To get past the court ruling in Texas v White, a secessionist only needs (a) a newer court ruling, or (b) to satisfy the ruling’s “consent of the states” clause. Courts overturning earlier court decisions is not common, but they do refine earlier decisions quite frequently. (b) does not explicitly require a constitutional amendment, though that would certainly work. I suspect what would happen, should a state decide to secede, is they would ask Congress to pass legislation affirming their right, and, should it pass, opponents would then challenge it in the Supreme Court, where Texas v White would either be refined or overturned.
Some US states, such as New York and Vermont, have the right to secede explicitly written into their ratification documents. (Amusingly, Vermont itself seceded from New York.)
I don’t think Calexit is going to happen soon – especially since it seems to be a Putin plot – but it would be easier than the process seems to be in Spain, and certainly the process leading up to it would be less bloody than the horrorshow we’ve seen in Catalonia.
