Two things:
One, we know we likely won't be happy with any ending Bioware writes now. We hope we will be satisfied though. Even if only a few of the promises originally made are reflected in the new ending, and not all of them - even if its still bittersweet - so long as its a more satisfying ending, the majority of this hate will die down.
Two, Mr Levine would do well to remember who funds his games. No, this is not a threat or a warning, and I honestly respect his opinion, but who funds Bioshock? It certainly isn't purely Irrational. If Irrational earned no money of the next Bioshock game, there wouldn't be another after that. The buyers fund the games, and if the buyers don't like the game, they won't buy. Games aren't purely art unless their done Indie for fun. As soon as you start putting profit margins, and need to earn money off your art to keep it afloat, it is a product. People don't like it, they won't buy it, and you won't get to make more art. Its the way things work. It is a better idea to fix a small thing about your art that gets many upset, and keep their loyalty to purchase more of your art, so that you can keep making art, rather than standing by what you think is right on principle, and being unable to make art again as nobody will fund it. This is how things work when you start using other's money to make your games, and Bioware owes us for our money. We don't think we're satisfied, we'll take our business elsewhere. It is a perfectly reasonable thing to do, and really we're being nice by asking Bioware to change the ending. We could just walk away and not give them money again. Instead, we're acting like a girlfriend who's about to break up with you, but tells you exactly what you need to do to keep her.