In the name of allah, the Beneficent, the Merciful What is sin in Islam?

Social Justice

It is indisputable however that the Prophet (saws) did not eat a lot of meat. A vegetarian diet is certainly in agreement with his sunna (saws). Take for example this hadith:

Yahya related to me from Malik from Yahya ibn Said that Umar ibn al-Khattab saw Jabir ibn Abdullah carrying some meat. He said, "What is this?" He said, "Amir al-muminin. We desired meat and I bought some meat for a dirham." Umar said, "Does one of you want to fill his belly apart from his neighbour or nephew? How can you overlook this ayat? 'You squandered your good things in the life of this world and sought comfort in them.' " (HQ 46:20). (Muwatta 49.36 under the title 'General Section on Food and Drink')

It is interesting that Umar (ra) in explaining this ayat would say "does one of you want to fill his belly apart from his neighbour or nephew" because we know that in this dunya at the present time, the gluttonous every-day consumption of mass-produced meat is responsible for famines and inequitable distribution of food resources. As Rafeeque Ahmed points out one person eating a meal of meat is actually eating 12 people's food because of the amount fed to the animal, the deforestation which allows them to graze and the use of water in the meat industry.

Eat and drink but waste not by extravagance, certainly (Allah) does not like Al-Musrifun (HQ 7:31)

To quote Dale Jamieson, "The addiction to beef that is characteristic of people in the industrialised countries is not only a moral atrocity for animals but also causes health problems for consumers, reduces grain supplies for the poor, precipitates social divisions in developing countries, contributes to climate change, leads to the conversion of forests to pasture lands, is a causal factor in overgrazing, and is implicated in the destruction of native plants and animals" ('Animal Liberation is an Environmental Ethic' in Environmental Values February 1998, p.48).
Stockpiling food while people go hungry is also forbidden in the Sunna:

Allah's Messenger (peace be upon him) said, "The table was sent down from Heaven with bread and meat, and they were commanded not to be unfaithful nor to store up for the morrow. But they were unfaithful, sorted up and laid by for the morrow, so they were changed into apes and swine." (Tirmidhi 5150 Ammar ibn Yasir)

'Apes and swine' is used in the Qur'an (e.g. 5:60) and hadith to describe the spiritual or actual condition of despised people. The current spiritual malaise in rich countries is exactly as described by the Prophet (saws) while the supermarkets and butchers are overloaded. Many Muslims cannot even get a glass of clean water to drink, while their brothers and sisters in rich countries eat like Kings! Malik Shabazz described the American practise of using surplus ships to stockpile grain until it becomes inedible in his autobiography (Autobiography of Malcolm X, Penguin, 1992, p.434). Humankind is materially the richest it has been in history, yet we are spiritually impoverished as half our population is materially impoverished also.

Eid

We know that half the world is starving because of the rampant consumption - including meat - by the rich. In the Prophet's time (saws), meat was only desired at Eid (see Bukhari 2.74 and 7.457 Anas). If the Prophet (saws) ate much meat other than at Eid, how is this hadith to be explained?

Umm Salamah said: Allah's Messenger, you necessarily develop trouble every year because of the eating of the poisoned (meat) of sheep. He said: Nothing befalls me but that which was destined for me while Adam was still a lump of clay. Transmitted by Ibn Majah. (Tirmidhi 124 Umm Salamah)

At Eid, those who could not afford meat were kept in mind:

I asked 'Aisha "Did the Prophet forbid eating the meat of sacrifices offered on 'Id-ul-Adha for more than three days" She said, "The Prophet did not do this except in the year when the people were hungry, so he wanted the rich to feed the poor. But later [when there was abundance for everyone, see Abu Dawud 2807] we used to store even a trotter of a sheep to eat it fifteen days later." She was asked, "What compelled you to do so?" She smiled and said, "The family of Muhammad did not eat to their satisfaction white bread with meat or soup for three successive days till he met Allah." (Bukhari 7.334 Abis)

And the welfare of sacrificial animals was also kept in mind. The Prophet forbade a number of pre-Islamic practices which he condemned as cruel including fara' (sacrificing the first-born):

The Apostle of Allah (peace be upon him) was asked about fara'. He replied: If you leave it (i.e. let it grow till it becomes a healthy camel of one year or two years, then you give it to a widow or give it in the path of Allah for using it as a riding beast, it is better than slaughtering it at the age when its meat is stuck to its hair, and you turn over your milking vessel and annoy your she-camel. (Abu Dawud 2836 Abdullah ibn Amr ibn al-'As)

The Apostle of Allah (may peace be upon him) forbade the devil's sacrifice. Abu 'Isa added in his version: This refers to the slaughtered animal whose skin is cut off, and is left to die without its jugular veins being severed. (Abu Dawud 2820 Ibn Abbas)

Artificial abundance

In the Prophet's time (saws), there was no artificial abundance of meat. Hormones and factory farming did not exist. Even so, the Prophet disliked that meat should become a staple. In stories about previous Prophets, the Prophet (saws) mentioned this:

Abraham...came to Ishmael's wife and asked her about Ishmael. She said, 'He has gone in search of our livelihood.' Abraham asked her, 'How are you getting on?' asking her about their sustenance and living. She replied, 'We are prosperous and well-off (i.e. we have everything in abundance).' Then she thanked Allah. Abraham said, 'What kind of food do you eat?' She said. 'Meat.' He said, 'What do you drink?' She said, 'Water." He said, "O Allah! Bless their meat and water." The Prophet added, "At that time they did not have grain, and if they had grain, he would have also invoked Allah to bless it." The Prophet added, "If somebody has only these two things as his sustenance, his health and disposition will be badly affected, unless he lives in Mecca." (Bukhari 4.853 Ibn Abbas)

Yahya related to me from Malik that he had heard that Isa ibn Maryam (Jesus Christ) used to say, "O Banu Israil! You must drink pure water and the green things of the land and barley bread . Beware of wheat bread, for you will not be grateful enough for it." (Muwatta 49.27)

Allah's Messenger (peace be upon him) said: A family which has dates will not be hungry. (Muslim 5078 Aisha)

Why does the Prophet (saws) say this? Because even though he lived in an arid region (Arabia), fruit and vegetables are good food. It is striking when reading the hadith literature to learn how hungry the Prophet (saws) and the Sahabah (ra) were (e.g. Muslim 7075, Tirmidhi 514 etc.). Still, a perusal of the books also shows that the Prophet (saws) preferred to eat fruit and vegetables.