Sort of for the same reason that they put fluoride into the water.
The makers of salt at some point came to the realization on their
own or were coerced (I don't know which) that hypothyroidism is
a problem.  Since many Americans use table salt frequently, they
could put it in their salt and nobody would notice any difference
in taste.

However, it IS possible to buy salt without iodine in it.  While
I personally don't understand the anti-fluoride brigade, I do
think that it should be possible to have non-fluoridated water
pumped into your house without having to pay extra for it and
without hassle.

--
Brian Evans             |"Momma told me to never kiss a girl on the first
bevans at gauss.unm.edu | date...But that's OK...I don't kiss girls."