Sex education is not simply a matter of public health and attempting to teach it in this way is damaging and dangerous to the sexual development of young adults.
An amoral approach that teaches sex education as part of a public health program separates human sexuality from its connection with love and emotional affection. This can lead teens to behave in a more promiscuous way. It can also inhibit their ability to detect sexual abuse and identify grooming behaviour.
Themes like love, value and admiration must be a central component of any sex education. These, unlike alcohol, tobacco, nutrition and exercise, are not matters related to public health. They are part of the emotional and moral development of a child and therefore fall under the educational purview of the parent, not the school.