Just because your immune system is fighting for your life against a parasite and doesn't have time for side quests doesn't make contracting a parasite good for you
If you count cells and genes instead of mass, every human hosts more non-human life than human. Call them parasites and delete them and die.
The argument was only to point out that just because labels are black & white doesn't mean life is black & white, and treating a label as reality is stupid.
No one went so far as to say "everyone should go get hookworm". That would also be a stupid thing to say, and more to the point: a stupid thing to think anyone was saying.