The human body begins collecting parasites from the moment they are born. Over time, more and more infect the body.
Young children have the least, old people the most.
The human body spends a lifetime trying to repair the damage done by parasites. Ivermectin rids the body of parasites and allows the human body to begin repairing the damage, if possible.
Do parasites cause cancer, etc? Maybe. More likely they simply don't allow the body to heal because all our bodily resources are repairing parasitical damages rather than fighting illness and disease.