Naturalistic Fallacy

Inferring what ought to be from what is — that because something is the case, it's good.

informal

The naturalistic fallacy derives a moral conclusion (what ought to be) purely from a factual state of affairs (what is), typically by equating “natural” or “how things are” with “good” or “right.” A description of how the world is doesn't by itself establish how it should be — this is Hume's is–ought gap.

Examples

“Competition for resources runs all through nature, so a ruthless, every-person-for-themselves society is simply how things ought to be.”
“People have always eaten meat, so it must be morally fine to do so.”

Why it works & how to counter

Persuasive because facts feel like they should settle values. Counter it by spotting the jump from “is” to “ought” and asking what moral premise would actually justify the conclusion.