As Chuck says, it's all about the application of common sense.
Most light a/c are just as visible with the landing light on or off, when you spot another machine during the day, what do you see? The silouette, which is dark. Why else are the RAF painting their high viz a/c black rather than day glo?
I must take issue with your assertation
Why would it be wrong to teach good airmanship at the beginning?
That is exactly what we teach. Think about your actions before you blindly follow orders, there are times that certain things are not appropriate.
In areas of busy traffic or poor viz then of course you should turn your lights on, but on a gin clear and sunny day in the middle of nowhere.........
Certainly in day time VFR in the UK we don't have to have all the light serviceable, so often when a light blows it is left until the next check. Would you then advocate turning the switch on just because you are supposed to?