After disputing the validity of the fine-tuning argument in a number of ways, Stenger presents us with an apparent difficulty:
It is rather amusing that theists make two contradictory arguments for life requiring a creator. …
In the fine-tuning argument, the universe is so congenial to life that the universe must have been created with life in mind. But if it is so congenial, then we should expect life to evolve by natural processes and a sustaining God is unnecessary.
In the second argument, the universe is so uncongenial to life that life could not have occurred by natural processes and so must have been created and be sustained by the constant actions of God. (God: The Failed Hypothesis, 163ff)
So, which is it? Well, both, when rightly understood.
There is an interplay of nature and grace that is so familiar to us in theology. Nature may well be very congenial to life, but even that may not be enough. The fine-tuning may be necessary for life but not sufficient. But given God’s grace (working with nature) and maybe an occasional miracle (working against it), life could have arisen and did, in fact, arise.
Equivalently, we can say that the universe is uncongenial to life without infusions of grace but would be much more so — so much that grace could not be given at all — if it were not fine-tuned.