I don’t consider this contradictory in that iodine is a very potent anti fungal, anti bacterial, anti viral and can’t stand against iodine if we get it in sufficient doses.
Two important points. The first is that many metals, semi-metals, halogens (like iodine and chlorine) and nonmetals are either antiseptic or inhibit pathogen reproduction. However, that being said, while a little is good, too much can be very bad, even deadly.
In the case of iodine, the thyroid will uptake a finite amount, but if more is in the body it will be excreted as excess. Both too little, and too much iodine can result in abnormal thyroid metabolism.
There are components in soy, flax seeds, and raw cruciferous vegetables (broccoli, brussels sprouts, cauliflower, and cabbage) that counteract iodine. These components, called goitrogens, can cause an enlarged thyroid gland, also called a goiter. Thus, large amounts of soy combined with inadequate iodine intake can exacerbate iodine deficiency.
Typically the safe range for iodine consumption for a healthy adult is between 150 and 1100 micrograms a day.
There is some concern about OTC iodine supplements, as some are suspected of being contaminated with arsenic, which while carefully monitored so as to only exist in tiny amounts in drinking water (max 10 ppb), is far less watched in food and supplements.
Even a small amount can inhibit the immune system, dampening its recognition of novel pathogens, giving them a much better chance of establishing themselves. Then, when the immune system does recognize them, it overreacts, which can be very harmful in its own right.