I've always believed having an issue with utility monsters is either a lack of imagination or a bad definition of utility (if your definition of utility is "happiness" then a utility monster seems grotesque, but that's because your definition of utility is narrow and lousy).

We don't even need to stretch to create a utility monster. Imagine there's a spacecraft that's been damaged in deep space. There's four survivors, three are badly wounded and one is relatively unharmed. There's enough air for four humans to survive one day or one human to survive four days. The closest rescue ship is three days away. After assessing the situation and verifying the air supply, the three wounded crewmembers sacrifice themselves so the one is rescued.

To quote Nozick from wikipedia: "Utilitarian theory is embarrassed by the possibility of utility monsters who get enormously greater sums of utility from any sacrifice of others than these others lose . . . the theory seems to require that we all be sacrificed in the monster's maw, in order to increase total utility." That is exactly what happens on the spaceship, but most people here would find it pretty reasonable. A real utility monster would look more like that than some super-happy alien.