This is partly because so much depends on the individual farm, the soil, the weather, and so on. Research results therefore tend to vary, depending on the subjective inclinations of those carrying it out. It is also less toxic and smelly than dung. Likewise, the nutritional value and flavour of a carrot has less to do with whether it was fertilised with manure or something out of a plastic sack, than with the variety of carrot, how long ago it was dug up, how it was stored, and the weather while it was growing. The notion that organic food is safer than 'normal' food is also contradicted by the fact that many of our most common foods are full of natural toxins.
Parsnips cause blisters on the skin of agricultural workers.
Toasting bread creates carcinogens. Yet educated Europeans are more scared of eating traces of a few, strictly regulated, man-made chemicals than they are of eating the ones that nature created directly. To a certain extent, the kind of food we prefer eating reflects how we relate to nature. The ancient Romans distinguished between foods not as proteins v carbohydrates, or even meat v vegetables, but as cultivated v wild. Farmed animals were a more civilised food than game.