Everything in nature is good for some purpose. Even poisons are serviceable
 Immanuel Kant, Critique of Pure Reason (1791). copy citation

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Author Immanuel Kant
Source Critique of Pure Reason
Topic poison purpose
Date 1791
Language English
Reference
Note Translated by J. M. D. Meiklejohn
Weblink http://www.gutenberg.org/files/4280/4280-h/4280-h.htm

Context

“for what source of confidence could be found, if she, whose vocation it is to destroy error, were at variance with herself and without any reasonable hope of ever reaching a state of permanent repose? Everything in nature is good for some purpose. Even poisons are serviceable; they destroy the evil effects of other poisons generated in our system, and must always find a place in every complete pharmacopoeia. The objections raised against the fallacies and sophistries of speculative reason, are objections given by the nature of this reason itself, and must therefore have a destination and purpose which can only be for the good of humanity.” source