What it is
Keeps cured meat pink and botulism-free — a real safety function, done at industrial scale.
Why your biology objects
Under high heat, nitrite reacts with the amines in meat to form nitrosamines — DNA-alkylating compounds, and the mechanism behind the WHO's Group 1 classification of processed meat as carcinogenic. Your ancestors preserved meat by drying, smoking, and fermenting; char the edges of this and you've run the reaction yourself.