Why are Christian opponents of homosexuality not against adultery or fornication?

Being against homosexuality is a prejudice which has existed for centuries and still exists. Adultery is a form of heterosexual activity against which there is not such a lot of prejudice - its merely a complaint you are doing it with more than one person. The christian opponents feel the prejudice against homosexuality and use christianity to justify something for which there is no logical reason. After all teh bible condemns /justifies so many things that most people are selective in some way.