Actually, I wanted to say little about this issue. However, in response to the point brought by brother Hayohf Dickson. As he says "They believe they are dirty" Meaning Muslims believe that pigs are dirty animals and that is why they are prohibited to them. Yes, he got it right.
Pig is one of the filthiest any animals on earth. It lives and thrives on muck, faeces and dirt. Pig is the best scavenger that I know that God has created. For instance, in the villages they don't have modern toilets and the villagers excrete in the open air. Very often excreta is cleared by pigs. Right or wrong?
Some may argue that in advanced countries like USA and Australia, pigs are bred in very clean and hygienic conditions. Even in these hygienic conditions the pigs are kept together in sties. No matter how hard you try to keep them clean they are filthy by nature. They eat and enjoy their own as well as their neighbor's excreta.