Whilst a quantitative ontology is perfectly useful for scientific study, only a qualitative ontology can make the necessary (qualitative) value judgments that form the foundation of ethics. Even the ‘obvious’ idea that suffering is ‘bad’ is a qualitative (‘bad’) ontological (‘is’) statement.
And whilst a descriptive teleology is wonderful for observing how things ‘do’ tend to behave, only a prescriptive teleology can provide goals against which actions can be said to be ethical or not. The observation that rapists ‘do’ tend to have forceful sex is a descriptive (‘do’) teleological (‘tend to’) statement. But only a prescriptive teleology can establish goals with which rape can be said to be inconsistent.