Craig asserts that the physical constants in the universe are “finely-tuned” “for” human life. He is right in saying that if the physical constants were different then the universe would also be different, and hence human life wouldn’t exist.
We could say that any set of laws, X produce a result Y. If you change X then you cannot help but change Y. Whatever version of Y you look at, you will always find a corresponding “finely-tuned” set of laws X. Therefore whatever universe one looks at, the laws are finely-tuned to produce it.
Craig however states that the laws are “designed” for human life. I can only think of two ways of knowing this. The first is if we know that God created the universe for human life. We cannot accept this as Craig’s reason, as it would beg the question of the debate. The second way we could know if the universe was designed for the emergence of human life is if we knew human life is what was being “aimed” for. Now I don’t know how Craig could prove this to us, but simply saying that our set of laws X give rise to a universe containing human life Y is not enough.
To illustrate this, imagine dealing five cards at random. What was the chance that your particular hand was dealt? Pretty low! This would only be significant if you knew you were aiming in advance for that particular result.
Furthermore, our fundamental constants are not really perfect for human life. If evolution were re-run, would humans evolve again? We would expect similar organisms with eyes (the eye evolved five times independently), but there would not necessarily be humans. If the physical constants were different (or, incomprehensibly, different laws entirely!) we still might get “life” of another kind, perhaps even unimaginable to us. Even if we did not get any life, there may be possible universes that contain things that are far greater, beyond our wildest speculations.
So, in conclusion, for Craig to rescue his argument he would have to show that the “purpose” of the universe was to produce humans, and that there are no possible universes that contain anything more desirable than human beings. I don’t see how anyone could prove such a thing, and Craig’s argument fails.