If you have a kid who can do that, then I agree with you wholeheartedly. It sounds like you are advising him on the art of debate, so your son is well prepared. That was one of my concerns, and--if it matters--I'm persuaded that you're addressing it *well*. No worries there.
Certainly, contemplating all the intricacies of all the facets of the issue is NOT what they should be doing with their limited time! That's not the point of the test. On that we completely agree!
I'm more thinking of the kid who thinks there's some side the test wants the writer to take, and he tries to argue that position even though it ISN'T the easy one for him to write. The point here is that there is no "right" side, and it's often true that a student has thought more about something she herself believes in, and so would have an easier time writing it.
In the end, we agree that easy and quick are key! Whatever that looks like.
