The key distinction, then, is not the between homosexual and heterosexual sex; it is between marital and non-marital sex. Why? Because the Church never separates the unitive and procreative elements of the conjugal/marital act. The unitive component demands marriage; the procreative component demands marriage. Sexual intercourse is too intimately linked to love and life for it to be employed anywhere except the humanizing structure of marriage.
By the way, this "narrow" application of the Church's prohibition of contraception within marriage does not, on my reading, necessarily promote or prohibit any kind of sexual morality for non-marital sex acts. In other words, the Church isn't all that interested in how people can best fornicate, or how they can employ prostitutes with the least amount of damage. Jesus didn't argue with the Pharisees about details regarding the disorder of divorce, and the Church doesn't legislate details over sex that takes place outside of marriage, either. She calls us to conversion.