Doctor Who episode 397: Genesis of the Daleks – Part Six (12/4/1975)
The nub of the episode, and the entire serial, comes down to the question of whether the Doctor has the right to wipe out the Daleks in their infancy. ‘You can’t change history! Not one line,’ he once said. Later, he modified that to the more ambiguous ‘I dare not change the course of history.’ He’s still struggling with that ambiguity, the idea that ‘some things could be better with the Daleks’, that ‘we’re all too small to realise [history’s] final pattern.’ On top of this, there’s a moral concern that by committing genocide the Doctor not only changes his own history, but his very nature – ‘I become like them. I’d be no better than the Daleks.’