They can be when they are converted into nitrosamines, which appears to happen in the absence of plants. In the presence of phytonutrients, nitrates are converted to nitrites, which have several health benefits. In the absence of phytonutrients, nitrates can be converted into nitrosamines, which are a potent carcinogen.

See: https://nutritionfacts.org/topics/nitrates/

Not sure what the parent comment is referring to exactly or if they are also conflating things but:

Nitric Oxide = NO

is not the same as common carcinogens in foods like

Sodium Nitrite = NaNO2 or Potassium Nitrate = KNO3

Not quite the same thing despite sounding very similar: https://www.mdanderson.org/cancerwise/what-to-know-about-foo...

(And good gracious, HN, how about answering the person’s question instead of downvoting it?)