[stordoff]

Just giving everyone the ability to vote isn't sufficient to make it a legitimate vote. You can skew the demographics in your favour by primarily promoting it in pro-independence areas (the Spanish government aren't going to lend it legitimacy by making sure everyone is aware of it). Furthermore, if you have a vote run by an unaccountable group who have a preferred outcome, what is to stop them re-running it, say, every week? Eventually the people who don't see it as legitimate will stop turning up, even if they did initially, and you will get a de facto independence majority.

FWIW, these are issues in theory with most elections. The difference is the organising party (i.e. the government) can be held to account (if voted out, they can't re-run the vote), and an official vote will have groups from all sides rallying around it so the demographics can't be skewed as easily.

[robhu]

Yes, referendums aren't held in a vacuum, the wealthy, powerful, and the government can use their resources to influence the result.

This happened in the UK with Brexit. The government opposed it, the bank of England, all the major institutions opposed it, the government spent millions on propaganda leaflets, and so on. It was unthinkable that the Brexiteers could win, and yet against all odds they did.

In this situation of course the scales are tipped similarly - while the regional government may want to spend on influencing the election, the financial firepower of the national government (who oppose independence) totally outstrips them, so if the referendum would be unfair it would be because it would disproportionately be tipped against independence.

It's not a perfect system - but a referendum is the best system available for answering these questions.