Thing is, how do we know there's no harm? If everyone does it, and the outcomes are pretty much standard, then you aren't to know if something is wrong. Just for eg, tummy upsets with the early introduction of solids might be considered "Just what happens when you start solids" if that's what everyones experience is. Do you know what I mean?
Anyway, I'm just thinking aloud.
But it's true, at the end of the day there are as many variations as there are children