What is the main reason of exchanging dowry?

The reason often stated while exchanging dowry is that the bride will be taken care of by the groom and his family for the rest of her life so in order to ensure a good start to her marital life dowry is given. It can be seen as a sort of a fee for marrying the groom and for the bride to be excepted by the groom's family. However dowry is a social evil destroying many lives every year. It is punishable under law and should not be supported.