There's some truth to that, and there are a number of other factors affecting our immune systems now that weren't in the past -- especially radiation; the fallout from the atomic bomb testing in the fifties and sixties will be suppressing our immune systems for many generations to come, not to mention more recent bomb tests on a smaller scale by various countries and leaks from nuclear power plants etc. Some of the chemical pollutants in our air and water and food suppress the immune system, too.
But in spite of all that ... if you look at the death rates from disease from a hundred years ago, before we started chlorinating the water supply -- especially for children -- children got all kinds of diseases and they either developed immunity or they died. Too many of them died.
Ah, the good old days ... my grandfather used to talk about how they had a water pump in the schoolyard with a dipper hanging from it and they all drank from the same dipper and "It never hurt us." I don't think I ever did get it through to him that it did hurt many of them. Every time one kid got sick the whole school got exposed to it, and some of them died of it.
-Cougar :{)