I get a little squiffed out thinking about it, but I'm in the minority, and I accept that. To your more general point: To me it's clearer to say that third cousins share at least one and possibly two great-great-grandparents.
Call me crazy, but I really think it's a good idea to go outside the family unit to seek a mate, regardless of genetics and such.Let's say that you meet a person with whom you share an immediate and mutual attraction.You date long enough that both are you are willing to have sex.To reiterate: what degree of known consanguinity is too close for your comfort?
Please assume for purposes of this thread that we're talking only about biological relatives. People willing to do their siblings should open another thread on another board, preferably a board that requires posters to write in Mandarin or Sanskrit. What would be more weird to me is if we were raised together from a very young age in the same household.
Sam's child Yvonnne is my first cousin once removed; we don't share any grandparents, but she is the child my first cousin (or, from her point of view, I am the first cousin of her parent).