Complex sentence: Hamer maintains that these microbes, rather than being antagonistic to the body, actually perform a necessary role in healing, and that some of the interventions of conventional medicine are counterproductive, by interfering with these natural processes.
Split into simpler sentences: Hamer maintains that these microbes, rather than being antagonistic to the body, actually perform a necessary role in healing. And that some of the interventions of conventional medicine are counterproductive, by interfering with these natural processes.