The idea was that people were deficient, which itself causes health issues, like low thyroid hormones, but I don't know how prevalent the issues were. I'm just saying it's weird that we didn't add it to water in lieu of chlorine, when ingesting chlorine has no benefit and may be harmful.

What's also interesting is that they're all halogens. So we've basically altered our intake of each through "public health measures," but to what effect....?