Well, debit cards are not accepted anywhere for car rental (at least I don't know any counterexamples). $260 in this case are returned at the end of the rental term, it is just a (relatively recent) additional service from Europcar, allowing people with only the debit cards to rent cars nevertheless. (Disclosure: I use Europcar at Barcelona airport about 5-6 times per year; they have some quirks, but I wouldn't use the terms "extortion" and "unethical").