I'm perfectly fine with whatever food choice you care to make, just don't be intellectually lazy and claim that vegetarianism causes no harm.
I have made no such claim - that's your strawman argument. Now, about those "unborn children": grains are seeds, and most grains and seeded fruits evolved to be eaten and digested by animals, so that a relative few of them would survive to propagate their species, either by surviving digestion or by being scattered when the animal feeds. Eating seeds while planting some of them is doing exactly what the plant "wants" to happen, evolutionarily speaking. Root vegetables are indeed another story, but since there is zero evidence that they can think, feel pain, or suffer in any way, your parroted argument collapses - doing harm to something that can't feel it and doesn't know it is only really harm if the species itself is harmed. And we do replant root vegetables as well, believe it or not.
Last, humans evolved as omnivores. It's quite true that we do well with small to modest amounts of meat, but it's also true that we don't need
meat. After half a century of folks opposing vegetarianism by squawking about having to "combine proteins" in order to get "complete protein," it has finally become understood that, given a reasonable variety of foods in the diet, there is no need to combine any of them. Given the amount of meat in the typical Western diet, we actually do far more damage to our bodies than we do if we refrain from eating it at all. So you'll have to forgive me if I don't think much of people who promote the health benefits of meat...while eating so much of it that they are harming themselves. It's rather like listening to an alcoholic spouting the benefits of a glass of wine a day.