If two species can bang and produce fertile offspring… // It’s one species.

I got another violation of this principle at home.
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The plant in the photo is a Capsicum annuum (bell pepper) x C. baccatum (ají / dedo-de-moça pepper) hybrid. It’s fertile; in fact the seeds from the fruit in the pic just sprouted. Following the principle you mentioned, and that I learnt as the definition of species, both parents should belong to the same species.

This shows biologists are using more criteria than just viable offspring to define species. But I don’t know which ones. (It also hints the matter is not racism, as it applies even to plants.)