Oneeyed is correct in his statistics.....
Read this article...and note the following-"Professor Alan Bittles of the Centre for Comparative Genomics in Australia states that the risk of birth defects rises from roughly 2% in the general population to 4% for first cousins and therefore that "It would be a mistake to ban it."[123] Researcher Aamra Darr of the University of Leeds has also criticized what she called an "alarmist presentation of data" that exaggerates the risk.[124]."
http://en.wikipedia.org/wiki/Cousin_marriage
As things stand-the US is the only country that bans it,and those bans vary from state to state.