Arsenic is not at all comparable to Iodine, it kills by severely disrupting metabolism, Iodine
has no such toxic effect.
I'm not sure you can call the 50mg or less usually recommended a megadose , theres no evidence for any cumulative toxic effects either, in fact quite the opposite
The body can make the distinction between things it needs to store and those it doesn't, why do you assume because it stores it then it is toxic?
I don't believe the body needs saturation with Iodine
to be healthy but I also don't believe it is harmful