Necropolitan
Hero
The Sycorax showed up with every intention of enslaving the human race, their first response to refusal was cold-blooded murder of diplomats, and then The Doctor threw a temper tantrum because Prime Minister Harriet Jones decided to shoot them while they were retreating and got her removed from power.the one that had the PM of England murder thousands of aliens who were running away?
The Doctor doing so got The Master elected Prime Minister and resulted in humanity being enslaved until a reset button happened.
It would be one thing if the Sycorax had surrendered and then been killed, but they weren't. They were retreating with no reason to believe they wouldn't just regroup and come back after The Doctor left. Which had happened previously and was in fact the reason Prime Minister Jones gave for shooting them.
Long story short Torchwood killed a ship full of unrepentant sadistic murderous slavers (all of whom were enemy combatants) who refused to surrender and in fact mocked the idea of compromise and peace.
There's a massive difference between that and Kate abusing her power as head of UNIT AGAIN by feeding a defenseless man to an alien.
There was no reason to do so other than sadism. It would be one thing if this was meant to be evidence of UNIT being corrupt (along with them using child soldiers, the nepotism, etc.), but it's not.