I'm not belatedly agreeing to that - I have never thought otherwise.
What goal posts have been moved?
You posted:
"The claim that the universe has always existed is likewise a belief."
Now the Universe means EVERYTHING. Including if they exist, Gods. Parmenides: "Nothing comes from nothing. So something has always existed". We are just arguing about what existed.
Of course, we don't know for sure that Parmenides's premise is correct. But we do know that if it is false, and something can come from nothing, this cannot logically be the result of something. EITHER the universe contains at least some eternal component(s), OR something can come from nothing. In neither case does positing a specific entity help to determine which case is correct, nor does it help us to grasp the reasons why things happened, or to establish a history for the universe. So, as I said before, we don't know the answer to the question 'Why is there something rather than nothing', but we DO know that 'because god(s)' ISN'T an answer to that question - it's just an unnecessary and un-evidenced additional layer of complexity.
We have a few proposals to consider:
1) The total mass-energy of the universe has always existed; But the Big Bang forms a boundary before which we cannot determine any details about what form that mass-energy took
2) The total mass-energy of the universe began to exist at or before the Big Bang, as a completely spontaneous event, which cannot have a cause by definition, as there was nothing to cause it.
3) Not only mass-energy, but space-time itself began to exist at the Big Bang. It is nonsensical to even discuss a 'before' or a 'cause', as these things cannot exist without time.
4) A part of the universe has always existed, and acted to create mass-energy from nothing other than itself; This contravenes the first law of thermodynamics, but we are assuming that the first law didn't apply at some point. The Big Bang forms a boundary before which we cannot determine any details, so it is possible that the laws of physics were sufficiently different to allow this to occur.
5) The part of the universe in (4) above was an intelligent entity that had a purpose for creating the rest of the universe. That intelligent entity then ceased to interact with the rest of the universe, and/or ceased to exist.
6) The part of the universe in (4) above was an intelligent entity that had a purpose for creating the rest of the universe. That intelligent entity continues to observe the rest of the universe to this day, and is really keen that we don't eat the wrong foods or masturbate, but is pretty 'meh' on the idea of rape, genocide, torture and slavery. We know of this entity through the writings of bronze and iron age peoples from one small area of the Middle East, and despite having no other evidence for its existence, or even for the existence of any possible mechanism by which it could interact with or observe matter at human scales, we assume that it is really real.
These six ideas are not exhaustive; Nor are they equally plausible. 1, 2 and 3 are all pretty parsimonious. 4, 5, and 6 all rely on the assumed existence of unexplained and un-evidenced entities for which there is no explanation as to why they remain undiscovered. 5 and 6 rely on the existence of intelligence without biology, which is something we can reasonably infer to be impossible - intelligence has only been observed in highly complex biological systems, that require very specific arrangements of mass-energy. Such complex arrangements can develop from pre-existing matter and energy over long periods of time by the action of natural selection, but their spontaneous existence without any such evolution is extraordinarily unlikely; their spontaneous existence from nothing at all is even less plausible, and the claim that this occurred is an extraordinary claim, for which we would need very strong evidence indeed, if we are to accept it. Supporters of this idea do not, however, provide strong evidence. They instead declare that evidence of any kind is not needed, and that belief in the absence of evidence is somehow virtuous. That, not to put too fine a point on it, is bullshit. And that they don't take the same approach to the hundreds of equally extraordinary, but different and incompatible, truth claims subscribed to by other religious claimants strongly suggests that they know it.
