Why you can't marry your relative?

United States
@jeiay41 (675)
September 7, 2009 7:58pm CST
I've been curious quite some time now thinking why this marriage is only for two different people without any blood relationship. I ask my mom about this and she said it a cousin married his cousin the baby they will created will be abnormal. So mylotters, what are you thoughts about this issue. I'll be happy to read each of opinion you had.