Furthermore, a man and a woman are by nature directed towards family life, for family is the basic unit of society
You're mixing things up terribly....
Mother nature doesn't care. The most base, natural sexual inclinations of heterosexual men and women are very, very different.... this is one reason that society tries to direct and temper raw sexual desire of both into the least damaging modes possible.
also, most human sexual contact is recreational rather than creational... only a tiny, tiny percentage of human sexual acts involve fertilization and only half of those reach the stage of implantation.
homosexuality is simply recombining natural human desires in new ways (liking recreational sex and emotional bonding with one's one sex) the differing nature of male and female sexuality also show up in the different ways that gay men and women prefer to order their sex lives.
People who prefer their own sex emotionally and romantically have existed in every human society and no punishment gets rid of it. It makes more sense to temper and direct it into socially constructive channels.
Since they cannot form a family, sodomites work to destroy it
People with no stake in the way a system operates have no stake in preserving it (why should they?)
Gay rights are about redirecting raw sexual urges into ways that can work for society (and giving gay people a stake in society).