The Doctor knows in his hearts; that some of his older faces wouldn't have done that. Sacrificing themself for a person.
He knows Oscar is right. And tries to block the memory of having seen Rose implode in this place and the aftermath of that. Of him being cold and cruel. If anything Oscar might get a sensation that those words are correct.

There's an exhale, "That's... one of the main reasons I'm attached to Jack. Part human. Part immortal."

Then a sudden feeling of fear; "That was an old face of mine. With jellybabies." Though he still enjoys those.

"And I'm quite tired of changing my face." Something about his voice sounds like a cat being rubbed the wrong way. "I love who I am right now. Thank you very much."