What does that mean? You can have MWI without Quantum Gravity. It just won't have any gravity.
If I had to guess, I'd say that you mean that you won't be able to get general relativity working just by doing quantum physics on a non-flat spacetime. You have to have the spacetime metric itself vary along different universes. This is true, and it seems pretty obvious. If you didn't do that, then gravity would have to be the same in all universes. But there's another universe where Earth is somewhere else, so the gravitational field obviously has to be moved.
I don't understand. GR describes the metric tensor through the Einstein's equations, relating (the) energy (tensor) and the metric tensor. If you grab yourself an empty universe, then put some stuff in it, then do the incredibly hard math (this step usually goes wrong) out you get a metric tensor. In QM the energy is given in terms of the wave-function. You claim that the observation that the earth's gravity pulls us in the general direction of the earth is inconsistent with the idea of putting the full wavefunction's energy into this equation?
What is something you used to believe, preferably something concrete with direct or implied predictions, that you now know was dead wrong. Was your belief rational given what you knew and could know back then, or was it irrational, and why?
Edit: I feel like some of these are getting a bit glib and political. Please try to explain what false assumptions or biases were underlying your beliefs - be introspective - this is LW after all.