Requiring labels on food is a proper role of government.
No it isn't. Especially not on a federal level.
Essentially, a proper role of government is to enforce contracts.
I agree.
Labeling food is really a contract.
No, it isn't.
For example, I have a good friend who is deathly allergic to mushrooms. If she eats a mushroom, then she goes into anaphylactic shock. She has to read all the labels on the foods she buys. If a producer would put mushrooms in a product and mislabel the product, then she would have a legitimate legal remedy to sue the maker of the product for damages.
I'm sorry for your friend, having a mushroom allergy must suck. Mushrooms are delicious. If a company labels their product as mushroom-free and it has mushrooms, that is fraud and she would have a right to sue for damages.
Enforcing contracts is a proper role of government.
I agree, again, but labels are not a contract.