Question on microscopic parasites

Doc, why doesn't the Barefoot dewormer kill all the microscopic parasites? Bacteria, for instance? Other organisms? Or does it? I know you said you use the zapper for the viruses of the common cold. That has worked for me, too.
Is the answer to my question that of finding what will kill the microscopic parasites, and that might that be different natural substances for some or each of these parasites? Tho maybe some could be grouped as being killed by the same natural substance. Antibiotics are used to do the killing, I know. These bugs being grown in a petri dish, then a sensitivity done to see what antibiotic kills them. Why couldn't we do this with a natural substance? Antibiotics being natural substance, but destroying the good bacteria in the process meaning we have to replace it with a multi probiotic.
Thank you.
EDIT: Is this why some people use the colloidal silver for killing the "bugs"? I don't know for sure what you think about using colloidal silver.
Thanks, again.