Doctor Who: The Doctor's 5 Darkest Ever Moments
3. The Fury Of The Time Lord
The Family of Blood discovered why The Doctor had used the Chameleon Arch, instead of facing them, and it was because he knew exactly how to defeat them. He was just being kind. He was giving them the choice to change their mind, and show mercy. They continued to murder and pillage their way through 1913 England, so John Smith opened the fob watch, becoming The Doctor again.
Destroying the Family's ship, The Doctor ensured that they would do no harm in the future. Imprisoning Father of Mine in unbreakable chains, trapping Sister of Mine in a mirror dimension, casting Mother of Mine into a dying star, and suspending Brother of Mine in animation and using him as a scarecrow. The Doctor was described as having never raised his voice, which made his fury even more terrible.
The Doctor does not have a "no killing" policy, and many have lost their lives due to The Doctor's actions; but instead of simply allowing the Family of Blood to die, The Doctor ensures their suffering in a truly dark moment.