Actually too much can hurt, which is why the recommendation is a maximum amount rather than a minimum amount But 600 mls is right at the upper end of the recommended amount so is ok. Dairy is not a particularly healthy food as such, but is an easy way to get calcium with an average diet. There are heaps of other sources of calcium though, and too much milk particularly can interfere with eating enough solids, which provide all the other nutrients babies need, especially iron and zinc.