The problem with infinite regresses or eternal multiveses (although they might well be true) is that they don’t actually explain anything. Don’t get me wrong, the theories them selves, do explain things such as “fine tunning”, but the multiverse idea, as well as the infinite regress hypothesis, sounds like the kind of idea one might think up when you cannot find a good “physical explaination” for physical reality. It simply does away with an ultimate explanation and goes into a tangent of infinities. It doesn’t explain physical reality or the laws of physics, even if it explains our universe. In this sense, i find such theories to be shallow ideas.
The other problem is that an infinite of something, cannot be measured, therefore we can never know if an infinite actually exists; the answer will always be finite. Therefore the multiverse theory failed, emprically, before it was ever thought about. A finite number of universes can be measured, so I’m more inclined to take that veiw; but then we have to find some evidence of those universes within this one. A scientists can only suppose that there is an infinite of something, because it convienently fits the data, but that doesn’t mean that its the right idea. There is no good reason to think that this universe has come from and infinite of something.