Greece wants access to other people's money. Those people can demand pretty much what they like -- if Greece doesn't like /that/ they can borrow on the free market (and pay dearly for their CCC- rating).
Collateral must always be placed where those who lend the money can get at it if the borrower breaks the terms.
Germany was in no way alone in wanting collateral and the rest of the Northern EZ was fine with having Germany/Luxembourg in control of the "Treuhandfonds". But it could also have been placed in Hamburg or Helsinki and they would still have been okay with it.
(It was, as you might know, not to be placed directly under KfW but under the IfG in Luxembourg probably precisely so that it was not under Germany's /direct/ control.)
It should in no way whatsoever have been placed in Athens under Greek management, though!
Can we at least agree on that?