What kind of food are you buying that you don't know what's in it? What do you think might be in, say, a tomato, butter, eggs, spices and seasonings, cheese, cabbage, liver or chicken? Sugars, proteins and fats. I don't believe I've wondered what more than that is in the food I buy. I know certain fish have mercury in them. I just don't buy that kind of fish. If there are other kinds of fish, or poultry or "whatever" that have harmful and not "normally" found ingredients in them, I would want to know, but absent knowing, I'm not going to have a conniption over my ignorance of such a fact.
To answer you question, I don't know if there we have a right to know what's in food. I know that knowing the ratio of sugars, proteins, and fats in any given food item is conducive to healthy eating, but then I don't need a food producer to tell me those things, for it's widely available on the Internet. I don't have a "beef" to raise about food producers being required to share the ingredients/makeup of the food they sell, but neither do I have a problem with their not being made to do so. I'm certainly not worried that food producers may willfully put harmful ingredients in their products. I am sure they don't aim to do that because doing so goes contrary to their achieving going concern and profit motives.