Most western world hypothyroid is autoimmune. When you add extra iodine to that you basically trigger an autoimmune response in certain individuals. More than half of the cases of hypothyroid in the western world is probably iodine triggered. The balance is fine. Too much and you get sick. Too little and you suffer another type of hypothyroid.

A start of an autoimmune reaction can sometimes be reversed by taking away iodine.

Adding extra iodine on an already flared up response, fuel on fire and a destruction of the gland will start. The gland usually does NOT pull through an immune system response. It's not something to mess around with. If you eat salt with iodine you probably already get too much iodine.