Does rightness come in degrees, or is it all or nothing? Our language suggests that it's all or nothing. Compare the word "good." The comparatives are "better" and "worse." The superlatives are "best" and "worst." We do not have the words "righter," "wronger," "rightest," or "wrongest" in our language. (I don't know about other languages.) Goodness appears to be analog, while rightness is digital (or binary). Utilitarianism defines rightness in terms of goodness. (The good, it is said, is prior to the right.) It might be thought impossible to define a digital term such as "right" in terms of an analog term such as "good," but it's not. Utilitarians say that the right act is the act, of all those available to the agent, that maximizes the good. Anything less than the best is wrong. This is the sense in which utilitarianism is said (by its critics) to be too demanding.
Addendum: Here is a handout that I prepared for my Ethics students. It shows the different ways in which utilitarianism has been formulated by its proponents over time.
