Money is the backbone of life so it should be circulated among people. However, when it is begotten by money itself without paying real efforts that help in the construction of earth and in enriching life, it will be owned by a few people only, while the majority will be deprived of it. As a result, instability will spread in society causing grudge among people who will become violent towards one another. As you know, violence begets but violence, and Riba (usury), in one way or another, causes such catastrophic results which negatively affect the human society. This explains why the Prophet, peace be upon him, said in the Khutbah of the Farewell Hajj:    

(Behold! All Riba from Jahiliyyah is invalid, for you is the principle of your wealth, but your are not to wrong nor be wronged - except in the case of Riba of Al-'Abbas bin 'Abdul-Muttalib - otherwise it is all invalid.)

[At-Tirmithi]