Response to Hallie, "The Yuck Factor"

Hallie wrote that the "yuck factor" of animal experimentation, as well as examples brought up in class such as pedophilia and incest, is not enough to justify deeming it immoral. She says that, in the cases of pedophilia and incest, there may be a "yuck factor" because we have been socialized to view them as wrong, but they can also be proven immoral on more rational grounds. I think that pedophilia can be proven to be immoral, because it involves children who cannot consent, but incest between consenting adults does not seem to harm anyone, and I am not sure why we are morally opposed to it. As I brought up in class, there is the fact that children conceived through incest are more likely to have deformities, but that is not the only reason we don't like it. There is just something about incest that makes people feel uncomfortable. Hallie brings up the example of homosexuality, which I think is a good example of the "yuck factor". Many people would probably describe homosexuality the way I described incest; "there's just something about it that seems so wrong". "It's so unnatural". I agree with Hallie that these vague feelings of discomfort are not enough to deem something immoral. However, in that case I do not see why incest is illegal (and considered immoral). Does anybody have a good defense for the widely held claim that incest is immoral that doesn't involve the "yuck factor"?