Your body literally needs them to function properly.
Salt- contains chlorine -a halogen... and salt prescribed as part of the Brownstein protocol in rather large quantities compared to a natural diet.
Iodine and iodide- also halogens... halogens that are advocated to be supplemented in extreme amounts compared to any natural diet in Brownstein's protocol and this thread in general.
And yes, both salt (sodium rather, but sodium chloride works) and iodine are vital to healthy human function.
For a better understanding of halogens... Halogens: Information from Answers.com
I really think that iodine/iodide can be used healthfully without the risks that some people are taking with it.
MORE is not necessarily better... and can be genuinely dangerous in many cases with supplements. Just like taking too much of many vitamins can make you really sick...
Nutrition, Toxic Dosages and Side Effects of Vitamins and Minerals
Too much selenuim for instance is linked to "Diabetes, garlic-breath odor, immune impairment, loss of hair and nails, irritability, pallor, skin lesions, tooth decay, nausea, weakness, yellowish skin"