The only explanation science can offer, is that the cause was...nothing, nothing at all.
That's not accurate. What science says is that we don't know for sure, and may never know for sure. (many scientists currently think quantum effects are likely responsible, through research and discovery of experimentally repeatable effects, and because we've literally observed that particles do pop into and out of reality even in the hard vacuum of space).
This is a lot more rational and truthful statement that saying "a) We definitely know. b) It was god, further, it was necessarily the god of my chosen religion, not any of the different gods of 4000+ other religions on the planet".
>> The Big Bang theory, as commonly believed, is just as religious as any other theory,
No the difference between science and religion is that science doesn't require faith. it requires evidence, and the whole process is based on replacing hypotheses and theories for better ones when proven wrong.
Religion on the other hand starts out by saying it already has all the answers and explanations, and requires faith of its adherents to ignore the lack of evidence.