Immanuel Kant

Immanuel Kant was a moral philosopher who didn't believe in exceptions. He maintained that stealing or murder was wrong in all circumstances. As the Fourth Doctor explained, he might argue that "stealing sweets is wrong, [...] because if everyone stole sweets, there wouldn't be any sweetshops." (PROSE: Categorical Imperative)

When Sarah Jane objected that it would be wrong of the Doctor to kill a baby, even if he was destined to cause the Earth's destruction, the Fourth Doctor told her that she'd get along with Kant. (PROSE: Categorical Imperative)