But let’s say it were possible to change the past. By changing the past significantly at a spacetime point you make all persons causally connected to that point change, and, practically speaking, you make most of them disappear (because the set of those people includes all the children born in the old timeline that will either never have been born or will have had entirely different personalities in the changed timeline). IOW, in practical terms, depending on where you change the past, you’re making thousands, or millions, or billions of people disappear. How is that not murder?