People love to take the vegans down a peg or two. I guess they must unconsciously agree that the vegans are basically correct and doing the right thing, hence the defensive mud-slinging.
There's a bullshit article "Being vegan isn’t as good for humanity as you think". Like many bullshit articles, it's based on manipulating some claims from a research paper.
The point that the article is making is summarised by this quote:
"When applied to an entire global population, the vegan diet wastes available land that could otherwise feed more people. That’s because we use different kinds of land to produce different types of food, and not all diets exploit these land types equally."
This is factually correct, according to the original research paper which itself seems a decent attempt to estimate the different land requirements of different diets. The clickbaity inference, especially as stated in the headline, is that vegans are wrong. But that's where the bullshit lies.
Why? Look again at the quote. "When applied to an entire global population." Is that actually a scenario anyone expects? The whole world going vegan? In the next ten years, fifty years, a hundred? No. It's fine for the research paper to look at full-veganism as a comparison against the 9 other scenarios they consider (e.g. 20% veggy, 100% veggy), but the researchers are quite clear that their model is about what a whole population eats. You can think of it as what "an average person" eats, but no it's not what "each person should" eat.
The research concludes that a vegetarian diet is "best", judged on this specific criterion of how big a population can the USA's farmland support. And since that's for the population as a whole, and there's no chance that meat-eating will entirely leave the Western diet, a more sensible journalistic conclusion is that we should all be encouraged to be a bit more vegetarian, and the vegans should be celebrated for helping balance out those meat-eaters.
Plus, of course, the usual conclusion: more research is needed. This research was just about land use, it didn't include considerations of CO2 emissions, welfare, social attitudes, geopolitics...
The research illustrates that the USA has more than enough land to feed its population and that this could be really boosted if we all transition to eat a bit less meat. Towards the end of the paper, the researchers note that if the USA moved to a vegetarian diet, "the dietary changes could free up capacity to feed hundreds of millions of people around the globe."