Hare Krishna!
Many arguments are made in this respect, that as long as we don't cut the animal we do not incur sin.
In the Mahabharata, there is a verse which states that one who sells the animal, one who buys the animal, one cuts the animal,one who cooks the animal, one who serves the animal and one who eats the animal, all are bound equally by the chain of Karma.
But leaving the spiritual aspect of it, anatomically, the human body is not structured to eat animal flesh. Studies have shown the length of the intestine of a tiger is 4 times the length of it's torso so when it eats flesh the toxins in the flesh are not kept for long in the intestine and are expelled at the earliest. Also the concentration of acid secreted in the stomach is so strong that it burns the bacteria in the flesh. While in the cow, the length of the intestine is 12 times it's torso and so the food takes longer time to be expelled from the body. We have seen that the incidence of the Mad Cow disease (bovine spongiform encephalopathy) which occurred in the UK when the started feeding the cows, animal fat minced with fodder. The human intestine's length is 8 times the length of the torso and at best the acid secreted in the stomach by sear the flesh slightly and toxins remain in the intestine for a longer period causing a host of diseases due to surviving harmful bacteria in the stomach.
And lastly the saying 'You are what you eat' and 'What you eat today, you wear for dinner tomorrow' are absolutely true.
When an animal is about to be slaughtered, it instinctively knows and the emotions of fear of flight or fight are secreted in the body. And these same subtle emotions enter our our subtle body and make up our mind.
Even in the Chandogya Upanishad, it is said that the gross part of food that we eat forms our stool and is excreted from our body, the middle or core part of the food forms our flesh and the subtle part of the food forms our mind.
The violence in cutting and animal is far more than the violence in cutting the ripe vegetables or fruits is which are anyways going to fall of or decay.
But when we offer sattvic vegetarian food to the Supreme Lord before partaking of it, the Lord takes away the sin from the cutting of the vegetables and grains and fruits which are offered and gives it back to us as His Mercy (Prasad) for us to consume for our growth of body, mind and spirit.
Even Krishna states in the Bhagavad Gita that If you offer Him with love, a Leaf, a Fruit, a Flower or even a little bit of water, He accepts it, partakes of it and gives it back as His Mercy, Prasad, for us to consume.
Hare Krishna!
Comments
The acidity and speed of digestion of humans is suited to a vegetarian diet. We have long tracts and low acidity, like ruminating animals such as cows, unlike tigers and carnivores whom have short high acidity digestion.
Further, humans have digestive enzymes for starches etc. right in the saliva itself, unlike carnivores, indicating we are meant for digesting grains.