1) It is unethical vis-a-vis the Sahrawi people, who are forced to live under Moroccan occupation or in exile.
2) It constitutes an inappropriate sign of political support to the foundless Moroccan claims to the territory.
3) It is in violation of international law.
4) It is a waste of EU taxpayers' money. The EU is giving money away to foreign a government in order to get access to waters which are not theirs - completely to the contrary of what is EU fisheries practice.
The EU considers to pay Morocco to fish in occupied Western Sahara. An EU-Morocco Fisheries Agreement from 2013 would be both politically controversial and in violation of international law.
The international Fish Elsewhere! campaign demands the EU to avoid such unethical operations, and go fishing somewhere else. No fishing in Western Sahara should take place until the conflict is solved.