4. people feel so much better after ridding themselves of parasites
This is generally the case.
People like Moritz, and natural hygeinicists, have a nature bias. I think that is great, but we are not a natural species right now. In fact, half of the USA is overweight.
I think of parasites as a pathological condition.
In fact, a beneficial parasite would be a contradiction in terms. It would then be properly called a symbiont.