Doctor Who: 10 Worst Things The Twelfth Doctor Ever Did
6. Leaving Davros In The Magicians Apprentice
The Doctor's temptation to kill Davros is something that has stretched far back into Classic Who. As the creator of the Daleks, Davros has probably caused more death and destruction than anyone else in the universe, and it's understandable why the Doctor would consider putting a stop to him permanently.
In the Series 9 premiere the Doctor almost succumbs to this desire when he encounters a young Davros in mortal danger. While the Doctor does initially try to help, when he learns the identity of the child he leaves him to his fate.
The Doctor can be ruthless when it comes to dealing with his enemies, but to leave a child to die is cold and something you'd more expect to come from a villain - not the hero of the show.
Typically the Doctor is someone who often goes out of their way to save their enemies, including Davros himself in episodes like Journey's End.
While the Doctor does go back and save him, it's only after learning that this act of mercy would let him save Clara in the future. If not for that it's possible he would have never gone back to help, leaving a child helpless and afraid.