1. I'm not against vegetarianism or veganism per se, but I'm not against meat-eating either. However, humans are omnivorous. Ideally we should have a varied diet (e.g. lean meats, green leafy vegetables, Butterfinger cookie dough cheesecake bars fried in a vat of lard).
2. That said, some strict vegetarians and vegans act like they're morally superior to people who eat meat. They turn their personal choice into a moral crusade against people who aren't vegetarian or vegan. They become zealots for vegetarianism or veganism.
On that front, Tim Hsiao has defended eating meat. Speaking of Tim Hsiao, I just want to note it's hard not to appreciate his artful photos taken at fine dining institutions across the nation such as (to pick a random example or two) steakhouses and burger joints.
3. What's more, some strict vegetarians and vegans act like the medical science is on their side. That vegetarianism and/or veganism represent the side of the intellectual sophisticates. I've even heard some argue humans evolved to eat plants. That we're fundamentally herbivores. That sort of thing. It's usually at this point when I roll my eyes and order a hamburger: In-N-Out, give me your double-double please. On second thought, let's make it a 5x5. Thanks!
4. As far as the medical science goes, strict vegetarians and vegans can often suffer from nutritional deficiencies. For example, take vitamin B12 deficiency. That's one of the most common deficiencies in strict vegetarians and vegans.
a. Plants don't make B12. At best, some plants can absorb B12 like Venom absorbing Spider-Man, but that alone wouldn't be sufficient enough B12 for a strict vegetarian or vegan diet. Not unless we're talking about chowing down forests! (Save the animals or save the rainforests - a moral dilemma for vegheads?) The primary reason is because plants don't have the necessary enzymes for B12 synthesis.
b. B12 comes from animals and animal products. Meat, eggs, cheese, dairy, and the like.
c. If humans are fundamentally herbivores, then (to take one issue) why do humans lack the gastrointestinal fermentation processes which support the growth of B12 synthesizing microorganisms (e.g. bacteria, algae) when these are present in herbivores? Also, where's my extra stomach? (Ruminates the illusive ruminant.)
d. B12 is needed for the body to make DNA, red blood cells, nerves, among other things.
e. B12 deficiency can be pernicious. Strict vegetarians and vegans often don't realize they have B12 deficiency until it sneaks up on them after it already caused some damage (e.g. anemia, tingling or numbness in hands or feet, memory loss, losing the ability to keep veganism to yourself).
f. Hence strict vegetarians and vegans need to supplement their diet with B12 (among other things). Typically that comes in the form of higher doses of multi-vitamins with B12, foods fortified with B12, and/or weekly B12 injections. However, after age 50, give or take, it becomes more difficult for the body to absorb B12 through fortified foods.
5. Obtaining B12 (among other necessary nutrients) without eating meat or animal products is typically something a Westerner living in the comparatively affluent West can afford to do. You don't see too many people in developing nations who are vegans. And the ones who are vegans typically happen to be the ones who are likewise comparatively well-to-do in their own nations.
6. In fairness, some people overeat meat. (So says the guy who orders 5x5s at In-N-Out.) However, that's a separate issue.