Obviously you would still need some sort of judicial system to decide on a punishment fitting for the crime. I suppose I should not have used the words 'eye for an eye', I should have said that the punishment should fit the crime and should be decided upon on an individual basis by a jury of peers. I definitely used the wrong terminology.
Selling anything to anyone is not harming them as long as the ingredients listed are the true ingredients. If somebody is stupid enough to purchase gasoline and then start guzzling it without first finding the necessary facts about what gasoline does to your system then that is their own fault. Same goes for people supplying their babies with formula as in your example.
The simple fact is that people need to stop using other people's stupidity as an excuse for their own.
On the other hand, if the seller were to not list that gasoline was in the baby formula that you bought then he of course would be punished for harming your child.
You, just like everybody else, are accustomed to there being holes in the system, because this is what allowing for an infinite number of laws creates.
There are no holes in the law I proposed so long as you take on the situation at hand with a rational mindset and do not try to contort it into something it is not.