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").
Well in this case at least this €260 was not going to be refunded. It was a one off charge. And I have rented many cars elsewhere in Europe using only a debit card.
OK, this is called "prohibitory pricing". As in, "we really really don't want your debit card, but if it is an emergency, here's an option. Still, please don't". I tried to rent a car with a debit card a few times, and it was simply not accepted everywhere I tried, (Europcar in Barcelona, Hertz in Geneva and Copenhagen, Avis in Geneva).
In 2012 in Boston, Enterprise refused to deal with my (European) debit card. However, in general this is right: US standards of customer service are unreachable anywhere in the world, except probably Japan. To the US people expectations, customer service is simply nonexistent here. "And remember -- here in France, the customer is always _wrong_!"
