As early as their first incarnation, the Doctor "certainly disapprove[d]" of violence. (TV: The Gunfighters [+]Loading...["The Gunfighters (TV story)"])
When the Fourteenth Doctor and Donna Noble returned to Earth, they found that the human race had gone mad, as Stooky Bill had made everybody "argumentative and violent". (PROSE: The Doctor's Busiest Day [+]Loading...{"page":"8","1":"The Doctor's Busiest Day (short story)"})