Why you should not eat meat is also described in the oldest holy, religiose and philosophical scriptures that can be found on planet earth, like the vedic Manu-samhita and Mahabharata.
The self-created Manu has said that the man who does not eat meat, or who does not kill living creatures, or who does not cause them to be killed, is a friend of all creatures.
Manu-Samhita: Manu Smriti @ Wikipedia
“Meat can never be obtained without injury to living creatures, and injury to sentient beings is detrimental to the attainment of heavenly bliss; let him therefore shun the use of meat. Having well considered the disgusting origin of flesh and the cruelty of fettering and slaying corporeal beings, let him entirely abstain from eating flesh.”(Manu-samhita 5.48-49)
“He who permits the slaughter of an animal, he who cuts it up, he who kills it, he who buys or sells meat, he who cooks it, he who serves it up, and he who eats it, must all be considered as the slayers of the animal. There is no greater sinner than that man who though not worshiping the gods or the ancestors, seeks to increase the bulk of his own flesh by the flesh of other beings.” (Manu-samhita 5.51-52)
“If he has a strong desire (for meat) he may make an animal of clarified butter or one of flour (and eat that); but let him never seek to destroy an animal without a (lawful) reason. As many hairs as the slain beast has, so often indeed will he who killed it without a (lawful) reason suffer a violent death in future births.” (Manu-samhita 5.37-38)
“He who injures harmless creatures from a wish to give himself pleasure, never finds happiness in this life or the next.” (Manu-samhita 5.45)
“By subsisting on pure fruits and roots, and by eating food fit for ascetics in the forest, one does not gain so great a reward as by entirely avoiding the use of flesh. Me he [mam sah] will devour in the next world, whose flesh I eat in this life; the wise declare this to be the real meaning of the word ‘flesh’ [mam sah].” (Manu-samhita 5.54-55)
“He who does not seek to cause the sufferings of bonds and death to living creatures, (but) desires the good of all (beings), obtains endless bliss. He who does not injure any (creature) attains without an effort what he thinks of, what he undertakes, and what he fixes his mind on.” (Manu-samhita 5.46-47)
“By not killing any living being, one becomes fit for salvation.” (Manu-samhita 6.60)
Mahabharata: Mahabharata @ Wikipedia
“He who desires to augment his own flesh by eating the flesh of other creatures, lives in misery in whatever species he may take his [next] birth.” (Mahabharata, Anu.115.47)
“The purchaser of flesh performs violence by his wealth; he who eats flesh does so by enjoying its taste; the killer does violence by actually tying and killing the animal. Thus, there are three forms of killing. He who brings flesh or sends for it, he who cuts off the limbs of an animal, and he who purchases, sells, or cooks flesh and eats it–all these are to be considered meat-eaters.” (Mahabharata, Anu.115.40)
“The sins generated by violence curtail the life of the perpetrator. Therefore, even those who are anxious for their own welfare should abstain from meat-eating.” (Mahabharata, Anu.115.33)
Bhishma started, “Numberless discourses took place between the Rishis on this subject, O scion of Kuru’s race. Listen, O Yudhisthira, what their opinion was. (Mahabharata, Anu.115.7)
“The highly wise seven celestial Rishis, the Valakshillyas, and those Rishis who drink the rays of the sun, all speak highly of abstention from meat.
The self-created Manu has said that the man who does not eat meat, or who does not kill living creatures, or who does not cause them to be killed, is a friend of all creatures. Such a man is incapable of being oppressed by any creature. He enjoys the confidence of all living beings. He always enjoys the praise of the pious. The virtuous Narada has said that that man who wishes to multiply his own flesh by eating the flesh of other creatures meets with disaster. (Mahabharata, Anu.115.9-12)
“That man, who having eaten meat, gives it up afterwards wins merit by such a deed that is so great that a study of all the Vedas or a performance, O Bharata, of all the sacrifices [Vedic rituals], cannot give its like. (Mahabharata, Anu.115.16)