> I'm not sure that conventional human mathematics lacking the ability to explain something indicates another abstract level of complexity above what we call "the universe".
I just bring up mathematics as an example of something that philosophers have typically categorized as "necessary truth". For example, 1 + 1 = 2 is necessarily true (there is no possible world in which it is not true) and as such requires no additional explanation as to why it's true (aside from just defining terms).
The fact that the earth is populated with living organisms is a contingent fact. That is, it is possible that there be no living organisms on the earth (or, in philosophical parlance, "there are possible worlds in which the earth is not populated with living organisms"). It seems perfectly logical to conclude that if there are living organisms on the earth, but there need not be, then therefore there must be some explanation as to why it is so. Indeed, one might say that the entire enterprise of science is predicated upon the notion that contingent facts have causal explanations.
So when it comes to the question of "why does anything exist at all, rather than nothing?", I think it's fair to question whether we can know the reason, but it likewise seems inescapable that there must be a reason.
> Also I don't know that infinite regress is necessarily a problem. Cycles most immediately come to mind, aka "loop quantum gravity".
Well, I can say that it doesn't look like the universe is headed in some kind of loop (because of accelerated expansion) but that (at best) answers the physical question whether we are in a cycle, not the metaphysical question of why there must be a prime cause. I admit I don't have a good answer for that, but I will certainly think on it. I also don't know enough about loop quantum gravity know how that relates (though I trust it does).
> That being said, I see no reason to abstract things more than needed.
As the saying goes "a theory should be as simple as possible, but no simpler". In this case, I would say that a "prime cause" is the simplest theory available. To posit that the universe exists without cause is too simple, and alternative theories (such as the multiverse theory) are more complex.
> "Prime cause" just appears a very fallacious argument to me, I guess that's the point. No offense intended.
No offense taken! It's always great to hear what parts of my thinking other people find unconvincing. I like knowing how other people think about these kinds of issues.