Thank you for your reply and for the very reasonable question you ask. I think correcting eyesight with spectacles and using enhanced fertility techniques is clearly different from a natural morality perspective. We need to do some distinguishing.
First of all it is clearly natural for human beings to have children. But at the same time it is not a necessity that a sexual act always results in a child. Children have always been a 'gift', not a necessity; this is also the way most parents describe their experience of having children. Eyesight is not primarily a gift, it is a part of normal functioning. So here is a first clear difference.
Secondly, in humans there is a natural link between the sexual act and procreation. This has a deep significance, because it means that a union of love between two people lies at the origin of every human being. It is clear that every act of artificial insemination and fertilization separates this natural link between sexuality and procreation. In the case of spectacles improving your eyesight, there is no question of any natural process being interrupted. This is a second clear difference between the two situations.
In a broader perspective, it is good to reflect further on the fact that procreation is not only concerned with the 'functioning' of a human person, but actually with the origin of a new person. In the case of natural procreation, this person is the result of an act of love of two people. In the case of artificial procreation techniques, the person results from a technical act by a biomedical expert. The act of procreation becomes 'dehumanised'. It therefore profoundly affects the natural origin of the new person. Spectacles have no such implications.
So natural morality can distinguish clearly between wearing spectacles and creating babies in test-tubes. If people in ecological movements can distinguish what is good for the nature around us, why can't we apply our reason to distinguish what is proper for human nature? It seems to me that such a path would keep us safe from much 'natural resistance' that manipulation would incur – and be the happier for it. Don't you think that if you applied yourself to the question, you could lead us there, Julian?