Tony, you are falling at the seemingly unsurmountable human hurdle - short term thinking.
You may be fine and outliving your forefathers, but nature works on a much longer time scale and we dont really know the long term effects we are passing on to our children who in turn pass it on to theirs etc etc.
For the record, while I like the general approach of the paleo, I dont jump into these things boots and all, but take an approach of gradual change to anything I do - nature has shown that sudden changes often come a cropper after an initial period of improvement - fad diets being a good example.
In this regard, our change to a grain based diet over the last 10 000 years has been IMO a relatively gradual change in natures terms, but significantly more dramatic has been the very recent change to highly processed grains that are milled and then stabilised chemically to preserve them till we get round to using them. This has all happened in the last 100 years or so - a flash in the pan on natures time scale, and to my mind far more damaging than the previous 9900 years of grain consumption where grains were generally stored whole after harvest and then ground as and when required.
A further recent and very damaging effect of modern food practice is the lack of seasonality. We tend to eat stuff all year round whereas in the past seasons dictated what we ate - ie stuff that was growing in the same conditions we were living in and therefore having appropriate nutrients for those conditions.
Personally, I think the human body can cope with all sorts of variations in the short term, but thinking long term, we need to be a bit more circumspect.
Unfortunately, we will not be around to see the results of our choices.
Yes,humans live longer now than ever before, but at what long term cost??
I suspect that our short term thinking is probably natures way of ensuring our own downfall as we get increasingly arrogant and play god without understanding the bigger, fuller picture, thereby ensuring the earth goes on long after we humans have shuffled off this mortal coil.
So, dont think that answers many questions, just my two pence worth