I’ve been thinking; are nitrites actually necessary for canned hams that are cooked inside their sealed tin, or is it only for the color stability and extended shelf life?
So, probably not "essential", but they do cut down the risk of botulism, and when producing 10's of thousands of cans of ham, a small chance of botulism could kill many people.
You can get fresh cured ham from an artisanal producer without nitrates (same for Bacon). Canned though... you'll probably want the nitrates.