No one has said we are not supposed to eat grains!!!! Its a fact that the grains (Wheat especially) that we eat are not the same as my 100 yr old grandpa ate. They have been genetically altered so bad that they are developing diseases or tolerances like Gluten. Gluten is not found in wheat from the 40's and 50's. Its was developed by genetically altering these grains to make them yield more per bushel. Wheat is supposed to be about 4' tall and yield "X amount" per bushel. Scientists altered the wheat and its now about 12" to 16" tall and yields about 2 to 3 times what original wheat used to yield per bushel. Gluten is a man made problem.
Do you have something to support this claim? Is it from Wheat Belly? I have read a lot about gluten intolerance and never come across this. And from what I know about gluten it seems very unlikely that it would not exist in wheat from the 40's or 50's.
Now you are correct that genetic engineering took place to increase yield. In fact, Norman Borlaug won a Nobel Prize for developing those high yield dwarf varieties of wheat.
There is, however, a less prevalent 'form' of gluten that has emerged from genetic engineering, glia-a9. It has more reactivity for celiacs and people with gluten sensitivity and is not as present in older varieties, so in a sense you are correct that man made it worse, but man did not create it.
The other problems that arise are 1) wheat is much less nutritious than it used to be, also due to genetic engineering, 2) the way it's produced is highly refined, not fermented, hard to digest. Even Weston A Price, who does advocate consuming grains, says to soak/sprout/ferment them so they can be properly digested.
Fact is, whether symptomatic or not, in many people gluten inflames the body, perforates the guy and causes a whole host of maladies. And here's the thing, there's no good reason to eat it. There is nothing it provides that can't be obtained elsewhere in more abundant amounts without the negative side effects. Not to mention the phytates in grains, but that's another topic.