One counter-argument to agriculture is Jared Diamond's classic article: "The Worst Mistake in the History of the Human Race"
http://discovermagazine.com/1987/may/02-the-worst-mistake-in...
http://discovermagazine.com/1987/may/02-the-worst-mistake-in...
People live to be 100 and happy and productive on largely grain-based diets, not thanks to the grain, but thanks to the modern world it allows. Pre-grain, we didn't live so long.
On balance I think grains are a no-brainer. Maybe there is some extraordinarily minor benefit to the individual not to eat grains, but, obviously, in light of the past 10,000 years of history, grains are fine for you and will keep you both alive and happy.