The reason for not taking is because of the low margin of error that is allowable. At close range a head shot can be taken quite easily as long as you know how your rifle shoots but further distances make it harder to be exactly on. This can lead to possibly wounding the deer. If you compare the size of a deer's brain to the size of the lungs and heart the brain is a much smaller area. Also at longer distances a bullet could be easily deflected by the skull depending on the power of the rifle and mass of the bullet. If you are to take a head shot you would want to aim between the eyes but up just a hair from the eye line. Many people have seen the consequences of making bad head shot leading to deer with broken off jaws or damaged faces leading to eventual starving that is the reason many choose not to. Although a bad shot at the lung/heart area can lead to a gut shot it is less likely due to the larger area the lungs/heart cover. It is all personal choice. It doesn't matter where on the body you want to shoot just make sure you know your gun and make ethical choices. I have shot 2 running deer in the back leg with a 12 ga. shotgun not wanting to but it happens although it seems unethical there is a main artery that runs along the femur that if hit the deer will bleed out very quickly. Although this kind of shot will ruin a lot of meat.