[austinjp]

Possibly a tangent, but I'd suggest that happiness and suffering are not opposites, so aren't both "x" in your function.

Someone might choose to maximise their personal happiness even knowing that their personal suffering would also increase (or even be maximised). Trite example: prisoner released from jail who sets out to kill the person who double-crossed him, knowing that he'll be re-incarcerated or even executed.

Happiness and suffering might be related but they're (somewhat) independent.