Vegetarianism is Unnatural
These two points are irrefutable:
1) We have canine teeth. Humans are designed to eat meat or we would not have canine teeth. If we were supposed to be herbivores we would have broad, flat teeth for grinding like an equine (horse) or other herbivore.
2) Look at anatomical plates and do some comparative anatomy. Humans have the GI tract of an omnivore, not an herbivore or carnivore.
BOTTOM LINE: Humans are DESIGNED to ingest (teeth) and digest (GI tract) animal flesh.
If someone "gets sick" when they eat meat, most likely they are HCl (hydrochloric acid) defiecient or lacking enzymes (protease, lipase) to break down meat. This is usually because of a damaged GI tract, aging, or from a prolonged period of refraining from eating meat.
NATURE DOES NOT WASTE MATERIALS OR ENERGY, so if we don't eat meat for a long time then we don't produce the enzymes (wasting energy, material) necessary to break meat down. Likewise, because NATURE DOES NOT WASTE MATERIALS OR ENERY, if we were supposed to be vegetarians we would NOT have canine teeth.
That is why vegetarianism is unnatural; it goes against our design, blatantly evident from our anatomy.