I, myself, think that we should give them back. It's there property, at first, if the UK didn't give them back because there was no museum to put them in, now that there IS a musuem, there is no reason not to give them back.
One of the main reasons we never gave them back was that Greece weren't looking after the ones they DID have. I am sure that it has been said before that if they looked after them properly they could have them back. I personally do agree with them going back to Greece, but giving back artefacts and pieces to their countries of origin is a major hot topic at the moment and it isn't as easy as that. You can't just click your fingers and have everything magically put back. I do think that they will end up going back to Greece, I just have no idea of what kind of time scale you will be looking at.