So as a response the opposition points out that veganism "morally" excludes certain nutrients as a way to call it an unhealthy/stupid lifestyle.
And there's technically a legitimate point to it IMO, maybe being pure vegan is nutritionally sub-optimal compared to some other options. Maybe kids shouldn't be vegan for ideal health. At the very least you have to seriously worry about various nutrients that you don't have to worry about with a less restrictive diet. But IMO that's like saying people into restoring/driving antique cars are driving sub-optimal vehicles. Yeah it's technically true, but that's their lifestyle/hobby so who cares?
And "malnourished" depends on your definition. It's no coincidence that we started growing taller and having more babies with the advent of agriculture. It's like putting a plant under a grow-lamp. Is the plant fueled by natural if imperfect sunlight "malnourished" relative to the plant under the grow-lamp?