My understanding is that, in general, our grandparents were healthy people. They certainly ate grains. So, what's wrong with grains?
Having been the chapter head of WAPF in Santa Fe for a number of years, and pretty Paleo now, I do understand that traditional ways of cooking (e.g. long slow fermentation of dough for bread) plus non-diet factors -- less stress, stronger family and community ties, hard work, being more in tune with the seasons, less poison in the air and in our food, and other factors -- contributed to their health.
Why do we make guesses about what paleolithic people ate when diet and health data from 100 years ago is much easier to get and doesn't make a case for eliminating properly prepared grains. What's changed in the last century that targets grains?