Saryn
External self-determination cares little about national laws. That's kinda the whole point. The real question is what type of conditions need to be met before a right to external self-determination arises and is recognized by other countries. In general, most countries don't recognize a right to unilateral seccession under any condition. At the same time, it is also agreed that if a state were to make the practice of internal self-determination virtually impossible or meaningless, then a right to external self-determination should arise. In which case any "no backsies" rule under US national law (even the constitution) may be seen as a breach of fundamental rights.
With independence, it usually comes down to who has the bigger stick (in both material and ideational terms). The are definitely scenarios in which US states can make a valid legal case for independence but the conditions for that still haven't been met as most international lawyers will agree that Americans in all states are afforded the right to internally self-determine. For now. Things are changing quickly.
Of course you pay it - just not directly - because there is basically no good from "within the country" whose inputs are not affected by the tarrifs.
The idea that the US is suddenly gonna massively ramp up its production of coffee, electric machinery, shoes and other products that are produced by countries with a massive competetive advantage is just ridiculous.