the Tenth Doctor being completely aware that his actions as the Time Lord Victorious are turning him into a monster, and still choosing to become one because there are worse monsters than him in the universe and he believes he's doing the right thing.
and to be fair, he is partly right and has a good reason to do what he does in this story, but the situation gets so out of hand and he grows so desperate that he uses methods that go against everything he stands for.
from 'The Knight, The Fool and The Dead'
