It's been legal in parts of the US and still is in a few states, but a general climate of distaste reigns over it, even in times when the marriage concept has been devalued.<quoted text>
While I'm sure you're not aware of this, first cousin marriage has been legal throughout England for the whole of legal marriage practices (it is thought that these marriages would also have been common in pre-legal religious marriages but less documentation exists on these) making these an occurrence that ranged from fairly rare for the small but growing urban skilled laboring class in the 16th century to quite common in rural and upper class through the 19th century and early 20th centuries. While they've grown less popular with the changing definitions of what a family member means, they continue to be legal here and have been a large part of the legal and cultural landscape for at least as long as marriage has been legally administered in England.
Consanguinaty (Sp?) has a history of restriction in the Western tradtion as old as that of first cousin marriage.
Beyond the obvious biological defeciency.