The reason this is illegal is because the violating team would be using more of the court while in team control in their front court than is permissible by the (intended) rules. The best example of this is the trapped player in the FC near the division line reaching back and bounce-passing the ball so that it touches the backcourt or the (division line) on its way to another A player in the frontcourt. If you're in favor of this being legal, then logically, you should be in favor of having the division line be in effect only as a temporary boundary, relative only to ten-second backcourt rules - after which, by the logic of such a play being legal, (and until the team going the other direction gains team control,) the division line would essentially disappear for purposes of rule applications.
Just my opinion, of course.
Edited to include: This would give a new meaning to the term "spread offense."
