"Leopold von Ranke, the father of modern history, described his discipline as 'an endless argument'. Never was this more so than in the case of Richard III."

Quite right. There's only one historical event which is beyond debate.

http://www.guardian.co.uk/science/2013/feb/04/digging-richard-iii-old-arguments

"A Holocaust, a Holocaust, my kingdom for a Holocaust" Richard III might have said, if he wanted his version of history to be the unchallengable dogma.

There are people who spend their spare time trying to rehabilitate Richard III, who died over 500 years ago - they are called "Ricardians". Inspired by their efforts, archaeologists have found Richard's bones. This is for the Ricardians a triumph comparable to Howard Carter's discovery of Tutankhamun's tomb. It's not that they say Richard was a good bloke, just that he was no worse than other child-killers of his time.

"Even if Richard did kill the princes in the tower, you have to judge him by the standards of his day - no other medieval king would have taken the risk of leaving them alive."

http://www.guardian.co.uk/science/2013/feb/04/richard-iii-dna-bones-king?intcmp=122

How far can you take this argument? Should we judge Genghiz Khan by the standards of his day? How about

"although Hitler murdered millions of people in death camps, you have to judge him by the standards of his day - no other dictator would have taken the risk of leaving them alive"?