Bingo! Moreover, even with beneficial things, there is a limit. It is possible to die from drinking too much water, or from too much oxygen.
Meat has been part of the human diet for something like two million years, whereas agriculture was discovered only about ten or twelve thousand years ago. Sugar was known in classical antiquity, but it was labour-intensive and expensive to refine, so conditions such as gout and dental caries were diseases of the rich until about a century ago, when modern industrial refining methods made sugar cheap for all. And industrial seed oils have been available for only a couple of decades longer than cheap sugar.
Given the archaeological evidence showing that agricultural societies are much sicker than hunter-gatherer ones, it should not surprise us that adding quantities of refined sugar and seed oils to the human diet might have deleterious effects.