You are incorrect about the improvement to herd health in free ranging deer. Do minerals benefit deer? Absolutely. Do mineral supplements benefit free ranging deer? There are absolutely zero studies to show that they do. All claims are based on penned deer and livestock studies. Deer clearly need minerals including sodium however, they have such a varied diet in nature, plants both native and planted become the delivery system. While an individual deer with a specific genetic or disease condition may benefit, the free ranging herd does not.
As for disease transmission, point source attractants increase face to face contact. Clearly there is face to face contact in an natural environment but at a lower rate. There are only subset of deer diseases that are spread this way. As I said, I don't think this is a large risk, but it is a risk.
Everyone needs to decide for themselves if benefits are worth the risk. That is certainly not the case for me, but everyone can decide for themselves, but the science is clear.
Unfortunately, Jack, you are simply wrong.
Deer crave the salt for osmonic balance in their blood. That alone is a benefit provided to wild deer. There is no argument against this simple fact. WHEN THE BALANCE IS OPTIMAL DEER DON'T CRAVE SALT.
Another study was done on selenium in an area lacking in this mineral. An artificial source of this mineral was found to increase the blood levels of local animals, including deer, to normal levels.
It is also well known that crops meant for human use, corn and beans and others, often deplete the local soils of needed minerals. Animals in the wild that eat these crops have been found to lack certain minerals (along with the domestic animals and humans). Supplementation helps to correct the problems (one of the same reasons we supplement domestic animals). While in the U.S. we are FAR behind in our attention to this mineral depletion, other areas of the world have been studying it for some time and actually actively return minerals to their farmed soils, in itself a form of supplementation. Areas of low magnesium, for instance, are well documented.
Will deer fall over dead without help? Nope, even without 100% of their optimum mineral intake. Will supplementation help? Yes. In areas where certain minerals are lacking, supplementation has been found to work on several species of animals.