Sure, how are they oppressed? In 1938 Barcelona was bombed because the army wanted to destroy the republic and what existed of Catalonia autonomy. So any existing Catalonia autonomy or democracy of any form was crushed in 1939, replaced by a military dictatorship, and only started to recover in 1977-1978. The Spanish dictatorship killed thousands of Catalans after the 1939 takeover.
The same forces in Spanish society who did that are the same forces which seek to destroy Catalan autonomy again. By the same means, policemen kicking down the door. You dismiss prior referendums, fine. There is going to be one in 11 days. So if those polls you cite are true, then it seems independence will not happen. It's bizarre to call a referendum in ten days "outrageously undemocratic", while decades of a brutal dictatorship established by an invasion and the murder of thousands afterward goes without mention.