Easterhay said:

But if Kurtz is to be believed, he would've gone with the downbeat ending to the film. We'd already had that with ESB. The story has to have a celebratory ending, like it or not, otherwise it's sending out completely the wrong message.

I do not see why it "has to" have a celebratory ending. The word Kurtz used was "bittersweet", implying a more mixed ending; not downbeat like Empire Strikes Back, nor essentially celebratory, which the original Star Wars film had already done, but something in between. It strikes me that this would have made a more thoughtful ending to the saga.