Generally, if the U.S. government is committed to an idea, that's my first tip-off that it is a bad one. At least, anytime since about 1913 when the statists and authoritarians took over.
Notice I didn't issue a blanket "grains are harmful". I stick to the blindingly obvious: processed sugars and highly-processed grains (and the foods they tend to be packaged in) are harmful. Even the government scientists will tell you that whole-grain bread made from freshly-milled wheat is better for you than Twinkies or that Wonderbread with a 2-month shelf life. Problem is, they still subsidize the hell out of the raw materials for Twinkies and Wonderbread. They would also (grudginly) agree that fresh vegetables picked that day from your garden are probably more nutritious than something harvested halfway across the country and shipped through three major distribution hubs before arriving at your local supermarket.
If you just look at things simply and empirically, it is very easy to test these questions. Problem is Americans are in love with "Science" as an overarching authority, and industry as a supplier of all needs, and would rather see huge edifices of logical supposition built upon studies done decades ago (of often questionable financial sources) rather than look at the evidence right before their eyes. Vary your diet for a month, and see if there's a difference in your health. Ain't that hard to do...