Doctor Who: The Doctor's 5 Darkest Ever Moments
2. "Kill Yourself."
Under the Salt Flats of Utah, in 2012, Henry van Statten captured a "Metaltron." Realising this is a Dalek, the Ninth Doctor ordered it to take its own life; ridding the universe of the scourge that is the Dalek race. The Dalek later responds by saying The Doctor would make a good Dalek - something that encourages The Doctor to fight the Dalek even further.
In 1975's "Genesis of the Daleks", the Fourth Doctor refused to commit genocide on the Daleks, yet the Ninth goes back on this, and orders the Dalek to destroy itself. Although The Doctor was suffering from PTSD of the Time War, and justifiably holds a hatred for the Daleks, this moment was shockingly dark, and was only prevented by the intervention of Rose Tyler.
The Doctor: All right then. If you want orders, follow this one. Kill yourself.
Dalek: The Daleks must survive!
The Doctor: The Daleks have failed! Why don't you finish the job, and make the Daleks extinct? Rid the universe of your filth! Why don't you just die?!