In my own family's past there was at least one cousin marriage, and probably more, in the late 1700's to mid 1800's. When I was researching this for a book idea, I stopped for a moment and thought about my male cousins. Would I want to marry any of them? Would I want to marry into a family that I already knew, in some cases better than I wanted too? No. But apparently many people did in the past and still do now.
Today, if you ask most people, the thought of marrying a cousin gives them the shivers. And not the good kind. Most people look on it with horror and equate it with incest. But it was once very common in the past and is a lot more common today than most people think. Right now the US is split 50/50 on the legality of cousin marriage. It is legal in Canada and throughout Europe to marry your cousin. Other countries in Asia, Africa, and the Middle East prefer cousin marriage. South America I couldn't find statistics for.
There are lots of websites out there on both sides of the issue and I'm not going to list them here. The primary argument against the practice seems to be the genetic one but when you look at the studies most could be used for both pro and con. The chance of birth defect or illness does not appear to be any higher than for the general population.
From my own research into it cousin marriage, particularly in the past when people were much more stationary, was one way to assure a person found someone to marry. In other words people married who was available. They married to keep property in the family or consolidate power. And they married because they loved each other.
Some famous people who were romantically involved with their cousins:
Albert Einstein (they were first cousins on his mother's side and second cousins on his father's side)
Jerry Lee Lewis
Franklin D. Roosevelt
Sir John A. MacDonald (first Prime Minister of Canada)
Christopher Robin (yes, that Christopher Robin)
Edgar Allen Poe
Mary and Joseph (first cousins)
Karen Blixen (Isak Dineson)
Johann Sebastian Bach
Werner Von Braun
Queen Elizabeth II
Catherine the Great
Isaac and Rebekah
Jacob and Rachel and Leah
John C. Calhoun
Oliver Wendell Holmes, Sr.
Samuel F. B. Morse
Nicholas and Alexandra
And the list goes on to include several signers of the Declaration of Independence, all sorts of royalty, and many other lesser well known people. Maybe it's not so taboo after all!