Board Thread:Spoilers!/@comment-25926288-20160915032911/@comment-24674051-20160926204714

Why goes back to Camelot and Dark Swan. Emma gave the Dagger to Regina to do what no one else would do if it became necessary. In that case, it was to take control of her to keep her from doing something stupid that she would regret.

In this case, it could be Regina doing what needs to be done (or at least what she thinks needs to be done) by taking Emma out of the Savior role for her own good. I'm still not convinced that Emma actually died in her vision (I don't care what the Oracle said, I don't trust her).