When you've eaten only little healthy food for a long time, your body is not only full of bromide and other toxins because the detox pathways will more than likely be damaged.
You will also be low in nutrients. Taking Iodine will nudge the body into repair mode and this will use up nutrients. If they're not there, you will be getting a hard time.
So ones reaction to Iodine will not only be linked to toxin status, but also to nutrient status.
Taking Iodine on a nutrient starved body will cause the bad nutrient status to go worse. Because of that, people will think the iodine is bad for them.
I have seen this with my mother. She refuses to eat differently from what she has been used to for the last 50 years. Strangely enough, she was raised on a healthy old fashioned diet. Her teeth are completely straight. Her parents were farmers and they prepared their own food from their own fields and live stock. But in her teens she developed a sort of contempt for that kind of eating. It was food for poor people. Well to do people ate white bread and processed foods. Unfortunately, that idea of feeling less than richer people has been deeply ingrained in her. She will not go back to poor peoples food.
As soon as she left home, she has put herself on a low fat, bad fat, high carbs, low nutrient diet. And it has been showing for the last 20 years. Her health is failing. All of her children have crooked teeth and bad health. My youngest sister is retarded and autistic.