Oh, my word!
KENT: Now look, you're giving me the biggest opportunity I'll ever have of ridding the world of this monster. Either I can convince you one way or I'll have to do it another.
DOCTOR: What you really want me to do is to kill him, isn't it?
KENT: What else do you do when someone is evil?
DOCTOR: Private justice, eh? Oh no, no. I'll expose him, ruin him, have him arrested, but I won't be his executioner. No one has that right.
KENT: Sometimes it's necessary.
DOCTOR: No.
"The Enemy of the World"
DOCTOR: What you really want me to do is to kill him, isn't it?
KENT: What else do you do when someone is evil?
DOCTOR: Private justice, eh? Oh no, no. I'll expose him, ruin him, have him arrested, but I won't be his executioner. No one has that right.
KENT: Sometimes it's necessary.
DOCTOR: No.
"The Enemy of the World"