One of The Doctor's consistent traits has been standing against oppression, especially from powerful institutions. They have repeatedly called out minor abuses of power as being a slippery slope and that just because someone is awful doesn't mean they deserve to die.
Like in Voyage of the Damned where the worst members of the group The Doctor ended up with survived while the best died.
As another character pointed out:
"Of all the people to survive, he's not the one you would have chosen, is he? But if you could choose, Doctor, if you could decide who lives and who dies... that would make you a monster."
In this episode Kate decided to become a monster. Her victim was a reprehensible person, but she still chose to abuse her power over life and death out of spite.
And the show glorifies it.
It says "It's good if the government violates your civil rights if you're a bad person. Conrad was a bad person and got what he deserved. The innocent have nothing to fear. Don't question authorities, they know better. Civil rights are less important than safety."
Every other time a character's said that they're the people The Doctor is trying to take down.
