> Also if all food producers radio tagged all food with what it was and its expiry date.
Nope, that won't make it work either. It would need foods packaged such that the fridge could tell if it is an unopened packaged (in which case see the use by date) - or it's been opened in which case see the "consume within x days of opening" date.
In any case, I ignore those and go by the test that predates all this "use by" and "sell by" malarky. It worked for my parents, and it worked for their parents, and ... I don't recall any of us getting food poisoning (very often).
Lets face it, things like cheese and yogurt are "milk that's gone off" (in a special way). If the cheese hasn't gone green and fury then it's still OK to eat. And my nose tells me if the milk (that isn't supposed to be cheese or yogurt) is going off.