That may be true, but the actions of homosexuals affect the society at large; the spread of AIDS is the perfect example of that. If their push for 'civil rights' means that religious institutions that oppose their lifestyle choice are forced to accommodate homosexuals while providing services for the general public, then that is an infringement on the Church's ability to conduct its activities.
Even though the Church teaches against homosexual activity, she also teaches that people who choose that lifestyle be treated with all Christian charity, and not suffer discrimination simply because of that choice. That does not mean that homosexuals should have preferential treatment, just that they not be treated differently because of their choice.
Just because it is also a religious issue, doesn’t mean the law may not also address it. On the contrary, a law which requires the equivalence of homosexuality is also a law establishing the practice of a religion, which is antiChristian.