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We'll disagree about whether teaching about human sexuality is central to the Gospel; but I readily acknowledge that human sexuality is central to each person's self-awareness, and of her or his relationships with God and with other people. Birth control, pre-marital sex, homosexuality, masturbation: few people get out of this life without wrestling with one or more of these.
The combox is not a place to do the history; but while Christian dissent about the sexual teachings of the church burst into public view at the 1930 Lambeth Conference, the theological, biblical, historical and sociological work that preceded it had been going on for at least a century. That may still seem "recent" in a church that is 2000 years old; but 2000 years from now it won't seem so recent and people will wonder why it took so long. 
The church has a rich treasury of research and experience from which to draw as it reflects on human sexuality; but it is boxed in by the false idea that it can't change.