You and I agree that human life is valuable and everything endangering it is bad
We know that some people's instinct can be against life, and is therefore fundamentally wrong - not a relative truth to be respected (you mentioned murder etc)
We also know that apart from instinct, people can become corrupted - they can gradually develop a disrespect for human life
Instinctive homosexuals cannot procreate
Instinctive homosexuals can corrupt heterosexuals
Open homosexuality is therefore anti-life
By accepting this in society, the individual triumphs over the collective. A pillar of human cooperation is removed. Suddenly more and more people start to do what they'd like to do, rather than what they should do. We retreat into ourselves. We care less about others. Experience becomes all that matters, not responsibility. Sex becomes not the sacred means of procreation, but a right to be enjoyed by anyone, in whatever way they desire, with no consequences at all. Birth control, anal sex, condoms, artificial insemination, abortions. More and more, life is denied and perverted. We become streamlined consuming machines, not humans.