I definitely think that if you were 100% confident in the simple MWI view, that should really dominate your altruistic concern.
TBH I don’t think this makes sense. Every decision you make in this scenario, including the one to promote or stop branching, would be a result of some quantum processes (because everything is a quantum process), so the universe where you decided to do it would be complemented by one where you didn’t. None of your decisions have any effect on the amount of suffering etc., if it’s taken as a sum over universes.
TBH I don’t think this makes sense. Every decision you make in this scenario, including the one to promote or stop branching, would be a result of some quantum processes (because everything is a quantum process), so the universe where you decided to do it would be complemented by one where you didn’t. None of your decisions have any effect on the amount of suffering etc., if it’s taken as a sum over universes.