No, as far as I know, no baby-food maker ever used rat poison as an ingredient. The point is that we don’t have to worry about it; if you have an infant switching off milk, you can shop the baby food counter confident that none of the choices will contain rat poison.
However, as a consumer, buying “green” is not quite so easy. Hastening the end of our civilization is a routine ingredient in most of the things we buy. By spending a little extra time and money, we can sometimes find alternatives that don’t contribute to our society’s destruction — though often not.
If baby food routinely contained micro doses of arsenic, of course you would go out of your way to buy uncontaminated versions for your child. But you would also recognize that we should not allow baby food to include anything so toxic in the first place.