The logic Steve uses, while true, fails to appreciate the benefit of selective ignorance.
It's possible to reason effectively about a system without understanding the turtles all the way down, as long as you understand the limitations of the abstraction you are reasoning in, which is possible to do w/o dissecting turtles.
I'd further argue that the "scientist vs engineer" personality distinction is applicable here. The scientist is concerned with solving the primary problem, while the engineer is concerned with optimizing all the turtles.
Take a physicist using Mathematica... does she need to know how compilers work to effectively do cutting edge work with the tool? No. So why is any other programming langage any different (unless you're amused by dissecting turtles).