> parasite must stop sucking blood for the host to survive

Biology doesn't work like that. Biological units are too selfish. It is an iterated game so evolution could affect how a parasite's children act. However defection is usually a winning strategy (because there's rarely enough coordination nor enough signals for cooperation to win).

Biology has amazing metaphors, but unfortunately most writers and readers don't understand biology well enough to use those metaphors as part of an argument.

The same issue occurs with other disciplines too.