According to an article that was posted on beliefnet.com by Adelle Banks, who incidentally I got to meet a couple of time while she wrote this article, Dr. Al Mohler has said that if science determines that there is a gene that pushes one into homosexuality and if science could create a resonable method to changing that gene while in the womb in order to determine that a child would be heterosexual, than that method should be employed in order to "unapologetically support the use of any appropriate means to avoid sexual temptation and the inevitable effects of sin".
While I generally find myself in agreement with Dr. Mohler, and while I am opposed to homosexual behavior and believe, as do many evangelicals, that it is outside of the intended relationship behavior that God designed for us to engage in, I also see this kind of thinking as ethically, and morally, irresponsible. To alter a child, in womb, who is not experiencing illness, nor is in life-threatening danger, is to delve into the realm of "playing God" it seems to me, and flirts far to intimately with altering the intended biological design that God created us to have.
If we reject the notion that we should alter any child who is created with abnormalities or physical defects than we should vigorously reject this type of thinking as well, I believe. I hope Dr. Mohler would rethink his position on this. We simply cannot oppose the efforts to "play God" when it suits our moral, biblical and ethical position and then do an about face when we feel it is appropriate to our moral sensibilities.
If you would like to read the article in its entirety you can do so here.