Doctors that recommend it probably take the "what harm could it do?" approach but really that extra iron can be very harmful to a bf babies guts and decrease the immunological effects of bf.
FWIW I really like my pedi but even I did not follow his advice on this.
We actually tried giving my DD Poky-vi-sol once and she projective vomited it. Never again.
You have to do what you feel is right but this is just MHO.