The referendum vote was illegal and goes against the Spanish constitution. Holding the vote was irresponsible, and the tactics used to promote independence have been misleading. 
The European Court of Human Rights decided against the pro-independence leaders who held the referendum, and have thrown the case out, on the grounds that it was illegal and the Spanish judges had every right to override the decision. 
Although all people do have the right to self-determination, many lawyers and legal experts in the Human Rights arena have argued that the Catalan people already have the required level of autonomy to fulfill this basic human right. Many devolved powers have already been given to Catalonia which satisfies the right to self-government. The right to self-determination is a principle that was meant to protect countries from colonialism and does not apply to ethnic groups within nations providing they are fairly represented. A historic ruling by the Canadian Supreme Court is often cited, in which the court found that the right to secede only applies in the case of colonial empires, the subjugation of peoples by alien powers, and in countries where the rights of independent groups are not recognized. Catalonia does not fall under any of these categories. 
Catalonia's right to self-governance has been recognized. The 2017 referendum was illegal and unconstitutional.