There is no "before the Big Bang", no before (as we understand it) before the creation of our world. Our brain cannot conceive the state of the universe at the moment of its creation. If there is a creator, he is obviously not bound by the limits of his creation. If you don't believe in a creator it's all right with me, but this is just as speculative as to believe there is one. You cannot prove or disprove the existence of a creator through solid science.
Is that really so?
Or is that just the sloppy traditional agnostic argument which really doesn't hold?
Your seem to put an EQUAL burden of proof on two arguments when in reality there is no such equal burden of proof.
If I claim that there is a Santa Claus living on the ice of Greenland, then the evidence of proof is NOT equal between you and me. I who have made the claim has to show the evidence, you need to do absolutely nothing but can call me an idiot until I have proven I'm right: Which I of course never will be able to.
The claim that there is a PERSONAL CREATOR behind the existence of The Universe is an equally idiotic statement until it is proven to be correct. But it is not a default position in a debate. Rather it just reveals the enormous need for a father figure, for a control over chaos, a banal urge, within the person who makes the statement.
This is why agnosticism never works in a debate. Because behind every argument presented, there is a PERSON with a specific need and a specific agenda. Statements do not exist without subjects. Which was precisely Zarathushtra's point: If you have your mind set on TRUTH and not on FALSITY, there will be a qualitative difference in your arguments, the very basics for science too. You and the statement are one with each other! That's Zoroastrianism!