That's YOUR definition of faith not the biblical one. Also, assumptions are not necessarily unjustified. They can be based on both jusifable inductive and deductive reasoning. Can we assume that from nothing comes nothing? Or can we assume that if there was nothing then nothing would exist? Or that if thee is something then there had to be something to cause it? I see nothing wrong with those assumptions-do you?
They are all very reasonable and I would have to accept them with a few
caveat.
-These assumptions are based on our experience in our universe, they might break down when dealing with something else.
-These assumptions are good until they get contradicted by facts, in which case, we will to reject or amend them (essentially, treat them as physical laws, I'd say).
For example, the assumption that 'nothing come from nothing' sounds pretty good to our non-relativistic brains but, in reality, we know that it is not true and that nothing does in fact
generate things in a constant manner.
But let's apply your argument where, I suppose, you intended to, the Big-Bang theory.
Your argument would therefore be that, nothing can not generate something, therefore something would have to have generated the energies in the Big Bang (and that would, presumably, be your Christian God).
The common answer to that is that, if we have a problem to account for the existence of an enormous but finite amount of pure energy, the problem would only be compounded by taking it a step further, one would you account for the existence of an infinitely (literally) vaster amount, not only of energy, but of complexly organized energy (a mind).
In order word, far from answering the problem, the injection of God only made it bigger and more unlikely... The assumptions just became infinitely bigger...
At this point, in my experience, apologetists will resort to special pleading (God always is outside of time and does not need an origin, which is as yet the biggest assumption of them all, I think) or invoke the mysteries they were so unsatisfied with a step earlier (if God is a mystery beyond our understanding, why wouldn't the origin of the Big Bang be?)
After all, possible explanations includes a -much- bigger and rarer version of a known phenomenon or just the idea that our initial assumption, nothing can come from nothing, is quite true in our universe but does not apply past the border of our universe after all, our models already indicate that our most fundamental physical laws break down and stop applying in the Plank epoch, why not this one too?