I am far less concerned with the arbitration issues than I am with the player development issues.
If LeMahieu is a bright, observant guy, someone extremely coachable and who is likely to learn from being in the majors simply by being there, and getting some infrequent playing time, then the call-up may make a great deal of sense. If he is going to get a good deal of playing time, and is not someone who will suffer serious confidence problems if he initially struggles, then the call-up may make a great deal of sense. But if he is still seriously raw and needs a good deal more time to develop the smoothness in the field and the pitch recognition and discipline at the plate required to be of serious value in the majors AND it is believed that he has the potential to acquire those skills with regular playing time, and the Cubs do not give him that playing time in the majors, then it is idiotic.
Hard to have a meaningful opinion on whether it is a good idea or a bad idea without knowing more about the team's scouting report on him (both physical tools and psychological/emotional makeup) and how they intend to use him.