In the present context I am asserting it as a presupposition
You don't get to, in any context. In general, because no unchallengeable premises are allowed here, and specifically in your case because you've never succcesfully defended it. You've been proven wrong about it in every thread I've ever read.
So defend the premise. I grant you that, if your premise is correct - that indeed, the account in Genesis is intended
by God to be an accurate, divinely-dictated account of what
actually happened - then indeed, no disagreement with it could be coherent. That argument is valid.
But there's no reason to accept your premise, so there's no reason to accept that your argument is actually
true. With an untrue premise, your argument is valid but not true.