The reason why it is forbidden to eat meat without draining the blood
Question

                Is there an obvious reason why it is forbidden to eat animals that are not slaughtered according to sharee’ah, such as those killed by electric shock or shot with a gun, etc.
Praise be to Allah.
    Allaah says (interpretation of the meaning): 

    “Say (O Muhammad): I find not in that which has been 
    revealed to me anything forbidden to be eaten by one who wishes to eat it, 
    unless it be Maytah (a dead animal) or blood poured forth (by slaughtering 
    or the like), or the flesh of swine (pork); for that surely, is impure or 
    impious (unlawful) meat (of an animal) which is slaughtered as a sacrifice 
    for others than Allaah (or has been slaughtered for idols, or on which 
    Allaah’s Name has not been mentioned while slaughtering). But whosoever is 
    forced by necessity without wilful disobedience, nor transgressing due 
    limits; (for him) certainly, your Lord is Oft-Forgiving, Most Merciful”

    [al-An’aam 6:145]

    Blood is the reason why it is forbidden to eat meat that has 
    not been slaughtered according to sharee’ah. Our sharee’ah intends that the 
    slaughtered animal should be drained of blood as completely as possible, and 
    that is because of the extreme harm that would result from eating its 
    blood. 

    It does not make sense, and it is unacceptable to suggest, 
    that Islam would set out all these conditions to get rid of the blood of the 
    slaughtered animal in the manner prescribed, then allow us to drink or eat 
    blood after it is drained from the animal. For this reason it is a definite 
    fact that Islam has forbidden blood as a means of nutrition for man. Rather 
    this prohibition is a clear sign of the wisdom and purpose of sharee’ah in 
    purifying the animal by draining the blood from it because blood is one of 
    the most evil and unlawful kinds of food, which the Prophet  (peace and 
    blessings of Allaah be upon him) was sent to abolish.  

    “he allows them as lawful At-Tayyibaat (i.e. all good and 
    lawful as regards things, deeds, beliefs, persons and foods), and prohibits 
    them as unlawful Al-Khabaa’ith (i.e. all evil and unlawful as regards 
    things, deeds, beliefs, persons and foods)”

    [al-A’raaf 7:157 – interpretation of the meaning]

    Al-Tabari said in his Tafseer: “ The phrase ‘blood 
    poured forth’ means blood that flows copiously. This is how Allaah 
    described the blood when He told His slaves that it is haraam. ‘Ikrimah 
    said: were it not for this aayah, the Muslims would gone to extremes in 
    avoiding the blood that remains in the veins as the Jews do. Al-Maawardi 
    said that with regard to blood that is not ‘poured forth’, if it has 
    solidified in the veins, as in the liver and spleen, then it is halaal, 
    because the Prophet  (peace and blessings of Allaah be upon him) said: 
    “Two kinds of dead meat and two kinds of blood have been permitted to us…” 

    The reason why the blood that is “poured forth” is forbidden 
    to us is because of the information that has become well known and well 
    established nowadays among the doctors and those who carry out medical tests 
    and study microscopic creatures, which is that blood is considered to be the 
    optimum environment for the growth of germs. So if a person drinks blood it 
    is as if he has drunk a “farm” for growing germs, in which the germs can 
    multiply and grow, producing lethal poisons which, as is well known, have 
    extremely harmful effects which result in germs invading the human body 
    resulting in the person contracting contagious and lethal diseases. 

    If it is said that cooking the blood and eating it will 
    surely kill these bacteria and microbes and put an end to them whilst 
    preserving the hoped-for nutritional benefits of the blood, our answer is 
    that some of these toxins cannot be altered by boiling and changed in such a 
    manner that they become beneficial to the body. There are some that do not 
    change at all, rather they remain lethal poisons even after being boiled, or 
    the heat may alter them in such a way that they become even more lethal and 
    harmful. 

    With regard to the benefits expected by the one who drinks 
    blood thinking that it is a nutritious substance that strengthens the body, 
    these benefits are non-existent, if we examine the composition of blood. 
    Blood is very difficult to digest, so much so that if some of it is poured 
    into a man’s stomach, he will vomit immediately, or it will come out in his 
    stools without having been digested, in the form of a black substance. The 
    reason why it is so hard to digest and it turns the stools black is the 
    presence of the red substance (haemoglobin) which is basically formed of 
    iron. As the blood passes through the digestive tract and as time passes, it 
    starts to disintegrate and break down, and thus it also harms the body. If 
    it were said that cooking also helps to break down the components of blood 
    and make it easier to digest and benefit from its nutritional value, our 
    answer is that boiling solidifies the proteins in the blood and makes it 
    even more difficult to digest, more harmful and less beneficial. 

    After hundreds of scientific experiments and huge 
    advancements in modern science, carrying out blood tests and precise 
    scientific research in this field, it has become indisputably clear to all 
    those who are concerned with human health of all nationalities and 
    specialties that the great harm done to health by eating blood or cooking it 
    and using it all boil down to the fact that drinking blood is ingesting a 
    lethal poison. This is clear from the following scientific facts: 

    1 – Blood is basically composed of two basic elements, namely 
    water which represents 90% of the liquid in which the components of blood 
    swim (which is known as plasma). The rest is formed of blood cells and other 
    elements. The one who wants to drink blood or cook it and eat it does so 
    because he wants to consume something with a high or regular nutritional 
    value. But these scientific facts prove that he would have to drink such a 
    huge amount of blood in order to avail himself of a small amount of blood 
    protein and a little bit of iron that it is not worth the risk of exposing 
    himself to the dangers that result from that. 

    In brief, blood is the opposite of what people think, it is 
    very poor in nutritional values. Therefore the fact that it is forbidden 
    does not mean that the Muslims are being deprived of any major nutritional 
    benefit. 

    2 – Major harm may result from this small amount of blood 
    protein mixed with very harmful and poisonous elements, which means that 
    ingesting it poses a great risk and puts a person in danger. Foremost among 
    these dangers is the poisonous gas with which blood is filled, namely carbon 
    dioxide which flows in venous blood from all parts of the body. 

    Because the one who drinks blood takes it from the animal 
    when it is full of carbon dioxide, which is a gas that kills by 
    asphyxiation. When a person dies of asphyxiation, it is because of the 
    accumulation of this gas in his blood, the lethal effects of which result in 
    death. 

    So it is obvious that repeatedly drinking blood which is 
    filled with carbon dioxide, on the part of one who is accustomed to this 
    practice, will lead to harmful results depending on the extent to which this 
    gas is present in the animal’s blood and the extent to which the body of the 
    drinker is susceptible to it. 

    What we have mentioned here are only the effects that result 
    from the components of blood on the one who drinks it or eats it after 
    cooking it. We have also mentioned other extremely harmful effects which are 
    directly connected to the specific functions that Allaah has created in 
    blood and the roles that it plays in the animal’s body, functions that 
    cannot be performed unless the blood is in a liquid, flowing state. If we 
    were to content ourselves with the above bad effects of using blood for 
    food, that would be sufficient to make any nation that appreciates knowledge 
    to promulgate laws banning this practice, even if that nation was kaafir. 

    “He grants Hikmah [wisdom] to whom He wills, and he, to 
    whom Hikmah is granted, is indeed granted abundant good. But none remember 
    (will receive admonition) except men of understanding”

    [al-Baqarah 2:269 – interpretation of the meaning]

    Glory be to the One Who taught the Prophet  (peace and 
    blessings of Allaah be upon him) that which he did not know and bestowed 
    that blessing upon him. Allaah says (interpretation of the meaning): 

    “Allaah has sent down to you the book (the Qur’aan), and 
    Al-Hikmah (Islamic laws, knowledge of legal and illegal things, i.e. the 
    Prophet’s Sunnah — legal ways), and taught you that which you knew not. And 
    Ever Great is the Grace of Allaah unto you (O Muhammad)”[al-Nisa’ 4:113]
Glory be to the One Who 
    honoured the world with this true religion which has not left any major or 
    minor matter without explaining to mankind the right way and the straight 
    path. Allaah says (interpretation of the meaning): 

    “Indeed, there has come to you from Allaah a light 
    (Prophet Muhammad) and a plain Book (this Qur’aan). 

    16. Wherewith Allaah guides all those who seek His Good 
    Pleasure to ways of peace, and He brings them out of darkness by His Will 
    unto light and guides them to the Straight Way (Islamic Monotheism)” [al-Maa’idah 
    5:15-16]