With infinite multiverses there is no such thing as morality.
If every possible universe exists then there are an infinite number of universes in which I am a saint and an infinite number of universes in which I am an axe murderer.
Even if at some level God has decided that axe murdering is a bad thing, if He has created a universe in which infinite copies of each person he created are axe murderers then it doesn't say much for the proscription against axe murdering.
It would be like the enforcement of speeding laws where everyone is pretty much allowed to speed most of the time and are only nabbed when they are speeding excessively or the odd occasion when the officers are overly zealous.
Or like the current "enforcement" of our immigration laws.
The nihilist holds that all is permitted. The multiverse theorist holds that all that accords with the laws of inflation and quantum mechanics is permitted. Either way, though, the notion that there's a deity that lays down and subsequently enforces a unique moral law fades away.
But in what sense can those "Doppelgangers" be considered to be actually you?
What's more, I hear people say, "I sure am glad I wasn't born in Ethiopia." In what sense would that person have been you?
One more thing. Say they perfected a matter transporter that seemed to work just fine on people. The way it worked is that it scanned you somehow, down to the very atoms and their states, and then transmitted that information through a wormhole to a very distant place, where the receiver reconstructed "you" down to the atom, out of raw materials.
Oh, and in the process, your atoms at the transmitting end would get disassembled and recycled.
Would you be willing to be 'transported' that way? Would the 'thing' on the other end have consciousness, or soul, or whatever? Would it be yours? Would it be you?
Uhhh, pass the bong, man.