If every food producer were to follow that dictum, no one would have to take responsibility. So everyone would be incentivized to break the rules.

And if anyone wanted to begin new a behavior harmful to others, they would only have to ensure others also do it.

Decisions have to made on values, not whether someone else is already doing it. If someone's getting away with a crime, it doesn't mean you get to do it, too. It still means neither of you should be doing it.