> But you have to delete the copy when you give the original back so what's the advantage?

You do in the USA? Why? AFAIK, not in The Netherlands. The copy was made from a legal source and in a legal way, and is therefore legal regardless if you do or do not possess the original copy.

Yes, in the USA you also have to destroy copies when you sell a movie or CD to someone. This is the whole point of copyright - to limit distribution. Otherwise running a rental service wouldn't be any different from hosting a download site.