Is there really any problem with an infinate regresion of universes?

[Whateverist]

why do you suppose infinite regress means "our" universe, whatever that means, fluctuates?

Because, if universes begin with a big bang from a singularity, as is commonly (but not universally) accepted, then the current universe must necessarily collapse in order for the next one to begin.

Philosophically, there's nothing prohibiting eternal universes. But, our observations so far indicate otherwise.

We are simply in no position to verify whether 'the' universe is the one and only or if multi-verses include our particular version.  We seem to be in no better position to rule multiverses out than we are to verify them.  But any perceived problems with infinite regress where cosmology is concerned all hinge on 'everything' having a beginning before which there was 'nothing'.  In general, we are ill equipped to draw conclusions regarding the infinite or eternal.  We (science) have gathered a lot of the clues regarding the origins of our neighborhood extending to the limits of the known universe.  What lies beyond is no more likely "nothing" than it is "everything else".  Until we find a way to peer past the limits of everything associated with the local big bang we will simply not know.  My gut tells me a frothy, foamy enormity of universes going on at a scale we will never be able to take the measure of.