I don’t get the comparisons to American independence. The colonists had no recourse but violence because they had no say in their government. “No taxation without representation”. Catalans may have taxation but they also have representation. Also, as others have pointed out, the leaders of the independence movement are far to the Left. Not a George Washington or Thomas Jefferson in the bunch.
American independence was about a lot more than just taxation. Likewise so is Catalonia’s independence.
As to your argument about representation the Catalan point of view is that the majority of Spain levies taxes on them, they have to pay, and the rest of Spain reaps the benefits.
In the USA due to the fact that people can write off their state taxes then the result is that families like my own who live in low-tax states are subsidizing the frivolous spending of high-tax states like California and New York. How am I represented in that arrangement? I live in Wyoming and I’m being made to foot the bill for California’s high speed rail, free education to illegal aliens, gun control, and etc.
The Catalans are leftists. True. But that doesn’t lessen their right to be free of a central government that bleeds them to eternally subsidize the rest of the country and the Madrid regime.