Jack Harkness never claimed to be a good man. He acts the part and everyone buys into it, but that's not, has never been who he is.
Jack Harkness is the man who bloodies his hands so no one else has to, carries rivers and lakes of blood in his past.
Jack Harkness is the man who gives the orders no one else will, who bears the condemnation, the horrified stares.
Jack Harkness is the man who does the math. Millions of children across the planet. One child he loves dearly, desperately.
The choice isn't easy, but it is simple.