Generally speaking, what about the person engaging in unnatural acts? Is he harming his life? Why does he have a "right" to harm himself? Where does it come from? Is his right to life violated? Does the harm to his life, health or soul resulting from such acts represent a loss to others as well as himself? Why does he have a "right" to harm or diminish society? Where does this "right" come from? Define rights.
Wow, so many questions in so little space. Is this leading somewhere?
To answer: The person engaging in the "unnatural acts" is doing so by choice. He may be harming himself. He has a right to harm himself. God obviously intended that he have that capability. else he'd have been created without free will. The right to harm himself comes from his self-evident nature as a free being. He can't violate his own rights. (Should he sue himself?) The things he does to himself may "hurt" others who want something from him. Your contention that he harms or diminishes "society" is just that, a contention. I'm not buying. "Society" is an abstract - the individual we're discussing, while hypothetical, is real.
Because someone with no right to harm himself has no option but to live life hidden under the bed, emerging for only just long enough to eat (the blandest and most non-fattening possible food) and perform other such absolute necessities.