Hi
I think there is some merit in concerns about over supplementing. I've seen more than one case of severe over-doing it.
That said, I believe some supplementing with calcium is critical if you are using crickets and other insects with the wrong calcium to phosphorous ratio. In nature, the wide range of bugs a chameleon would catch undoubtedly provides the balance of nutrients needed. In captivity, we're are providing a very limited number of bugs that are (in most cases) not what would be their native prey. In order to compensate for the inadequacy of our feeder insects, we supplement. And of course we gutload.
I dont dust every bug I give to my chameleons. For example, i never dust butterworms with calicum since they are naturally adequate in that regard. But I do lightly dust calcium on crickets, since even with gutloading they're just not up to snuff. Even though I offer at least 6 (and up to 14) different types of bugs in a given month, even though I gutload in the best way I know how, I still use a vitamin supplement now and then.
I dont doubt there's other ways, maybe better ways. But what Im doing seems to work for me / my chams. So I'm going to stick with my program.