My response to that poster would be , "Schaedenfreude, got to love it", so I am refraining. How did she miss the whole thread of all the purebloods being related that's been going on for the last three books?

First cousins squick me a little, especially if they've known each other since childhood, but second cousins outwards is fair game. At that level of consanguinity, the chances of matching harmful recessives isn't much above the general population anyway, IIRC.