Why do we teach IT? Because for most of us the simple act of linking a child to a creative activity, like programming, is profoundly satisfying. We teach IT because for most children, learning must be motivated, encouraged. Why do I teach IT? Because I find it one of the challenging subjects in the new curriculum. Why not. :-)
What is the role of computing in the classroom? In my humble opinion: primarily to prepare the child for what is about to hit him/her: real life. It, probably more than most high school taught skills, will give them a distinct advantage in a cut-throat world where you HAVE to be better than your neighbour to land a job. The role of computing is to give the child as much exposure and therefore experience before they enter the working/studying world.
That's my 2c's worth anyways. 