That's not true in all cases. Many people use bio-active soils in their vivariums, and get the soil started with unbaked logs and leaf litter that contain invertebrates. That being said, I don't do that. I bake all my leaves and tank decor before putting them in my vivariums, and I thoroughly wash all of the plants, roots included, of all the plants that make it into my vivariums. But you'd literally have to tear root structures apart and rip a lot of fine roots to COMPLETELY rid your plants of any soil. Believe it or not, most of the tiny invertebrates that will make it in the soil from the root bases of plants are harmless, they're only looking to eat decaying matter and to enrich soil. Despite sounding controversial, the reality is that most mites aren't even parasitic, and trust me, all of my geckos are completely mite free, and have always been mite free. If colonies of these detritivores make it into some of my tanks in the tangle of plant roots, so be it. Sheer stupidity? You should think twice before calling someone names, as I'm a very well-informed individual who spends a lot of time researching and applying husbandry techniques. I have never had a sick gecko, never had stool problems or mite problems with my geckos, and all of my plants and soils are healthy as. It's simply a matter of common sense, and if I ever have trouble with my animals from springtails that came in from the fine root-tangles of my plants, I'll be sure to let this forum know immediately.
Cheers,
-Matt