Getting back to your original post - about a year ago, I was discussing this on another thread, and some brilliant person pointed out that there is *not one example * of an intact and happy marriage, or even a good relationship, between a Wizard/Witch and a Muggle. Not one. And, since the children of Muggleborns and Wizards are considered half-bloods, it's pretty clear that true half-bloods, like Severus and Tom Riddle, must be relatively rare.
Just another double standard from Rowling, IMHO.
Just another double standard from Rowling, IMHO.