Taking advantage of any reproductive technique is both a subjective personal issue and an ethical issue. There are two issues involved in this particular question: dealing with sterility and attempting to have a child free from genetic diseases, which applies to both fertile and infertile couples.
The options for would-be parents who are unable to conceive have expanded in the past few decades to include medical manipulations of DNA that were previously science fiction. Questions about the ethics of such options hang in the air still and are added to when further steps are made. For many, the procedures of in vitro fertilization (IVF), oocyte retrieval, hormone therapy, egg and sperm donation, and nucleus transfer are unimaginable because of personal beliefs. Other people would be unwilling to consider surrogates. Still others would not cross their own invisible line and adopt, yet would undergo the previously mentioned procedures others balk at based on personal beliefs. Many of the reasons behind a person's individual choice include religion, experience, level of comfort with the procedures, finances, and how strong the psychological need to procreate is, including the need for it to be biologically theirs.
The ethics of the situation should look at the end benefit as well as the risk of the means. Is procreation necessary for the greater good? Is the personal benefit worth any personal risk? Starting with the easier question - The personal benefit outweighing the risk is dependent on what is actually carried out and subjective based on the health and state of mind of the couple (or woman) involved. This is why it has been so difficult for any laws on the matter to be passed. It is ultimately up to the person undergoing the procedure as to whether something that is not necessary for their health (i.e. elective) has acceptable risk, especially when the risk is minimal.
However, there is another factor at play for the context of this particular debate - the idea of manipulating the genetics of a potential fetus, not just to conceive, but to make it "better". This can not happen. It simply can't. Scientists could manipulate the genes they know for the diseases they know, but what about the diseases they don't yet know about? What about the minor alterations and how they affect the larger picture of who or what that child is? The doctor may eliminate the genetic alteration known to cause diabetes, but what if the child had that to counteract a different mutation they unknowingly have for an even worse disease. There would have to be a blueprint for humans to insure good health, but that still wouldn't eliminate the random mutations that occur while the fetus develops or the unknown diseases that may develop with environmental changes. There are also certain genetic alterations that benefit the population that has them, but dooms them when a virus or bacterium comes into contact with them. It would not be possible to make a child better without, in some way, making them worse, genetically speaking.
As for the question of whether procreation is necessary for the greater good - the planet is overpopulated. The environment is in danger according to many scientists. Yet we as humans feel a need to continue our lines. In one way this is necessary to propagate genetic diversity. In another way, it leaves the thousands of children needing parents to grow up in orphanages. When adoption is an option it would seem unethical to go to such extreme medical lengths to have a child. So, for myself, I would not go to such great lengths to reproduce. I don't need a "perfect" child, nor do I need to raise one made of my own DNA.
I do not think it is possible to guarantee a child free of genetic diseases. Even if it was, I wouldn't do it. For me, personally, it is an ethical line I can not see myself crossing. I would feel responsible for the child that did not get adopted, for the child that could possibly have an unknown condition, and for the waste of resources it took to create them.