The Death of Athelings...
I must say, this time through the story of the Norman Conquest I find myself surprised at how pro-William the Conquerer I have become.
It seems to me that the invasion of England was simply such a mad thing for a Duke of Normandy to do--unless he believed that the English throne really was rightfully his, by the choice of King Edward the Confessor, and that Harold Godwineson had betrayed him: he had rescued Harold from prison in Ponthieu, and Harold had then promised to support him as Edward the Confessor's successor. And William was not mad.
And it seems to me that King Edward the Confessor would have had to have been mad--or at least profoundly un-Anglo-Saxon--to not try as hard as he could to keep the family of the murderer of the Atheling Alfred off the throne. Hence Edward's choice of William as successor seems entirely logical.
Of course, after 1066 William found that he had bitten off a lot more than he could chew...