The medical community in general shuns supplements because of the intricate interdependence that exist. Many studies show Iodine supplementation exacerbates conditions in many people so they read the headline and take it at face value with out understanding why.
Supplementing Iodine when selenium deficient can cause problems.
As for salt in iodine, the amount in negligible at best AND it evaporates so by the time you get to the bottom of that 1 lb jar the Iodine content is much less than when it was opened.
Additionally upping salt intake often causes problems because it exacerbates the already prevalent poor salt to potassium ration that exists in almost everyone and the salt that has iodine added is also processed so contains copious chemicals and what not that are not beneficial to optimal health.