The Grand Ayatollah Makarem Shirazi answered questions about the reasons for pig meat being Haram.
Question: Why pig meat is Haram? Whilst like cow and sheep, (pig) has 2 piece hoofs and also with advances in medical science (including vaccines and special animal husbandry) it does not have diseases of the previous centuries?
The Grand Ayatollah Makarem: Pig which is popular with the Europeans who consume its meat more, is the symbol of having no zeal, and it is a dirty animal; pig in its sexuality is extraordinarily careless, and in addition to the effect of food on morality which has been proved scientifically, the effect of this food on carelessness in sexual matters is evident. In the religion of Moses (AS), pig meat is also Haram and in Bibles the sinners are likened to pig and in stories, pig is introduced as the symbol of the Satan.
Therefore, based on this definite principle which has been mentioned, the meat of any animal which has the characters of that animal and by the way of glands and their secretion (hormones), it affects the morality of those who consume it; and maybe one of the reasons behind the extreme carelessness about sexuality (sexual activities) in the western countries is the consumption of the meat of this contaminated animal.
Source: PERSIAN SHAFAQNA