From what I have heard, there is no agenda other than giving correct information, in state sex ed. Nothing is promoted, the idea is to be truthful and to help youngsters stay safe - which includes not having a sexual relationship before they are ready and being respectful towards the feelings and the bodies of others (& their own). Sorry that sounds clumsy.
When I was younger, heterosexual relationships - leading to marriage - were actually promoted. The vast majority of people were and always will be heterosexual but homosexuality must be discussed otherwise people will have odd ideas about gays, not to mention being overly, almost morbidly, curious.
It all seems quite healthy nowadays, people accept others for who they are and don't dwell on it.