What is the liberal ethical argument against necrophilia? (Harm vs disgust)

[America Needs R'hllor]

In addition to what everyone said, I think we have to accept that there are universal, human values rooted in our very selves that are normative and not dependant on any set of rules. Homosexuality is completely fine because it cannot cause harm by itself and is something a large percentage of humans cannot help but practice, and also because it was proven not to be a mental illness but is rather perfectly natural. Thus, people disgusted by homosexuality are a**holes and illegitimate.
Meanwhile, necrophilia and incest are clearly something we shouldn't do- the disgust for them is rooted deep within us, and they can indeed cause grave harm by themselves- incestous children are often born with defects, and necrophilia is a public health hazard. These behaviours are also a choice, and could be a mental illness too. There's a clear difference between the two cases.