The idea of America is that people should be free to live their lives without interference from an oppressive government. So long as we don't harm others, "the pursuit of happiness," however we define it individually, is the central tenet of our freedom.
Gays aren't seeking special treatment; they're seeking equality under the law. Right now there are special rules in place to specifically exclude homosexuals from the benefits of civil society. The repeal of these bigoted rules is the goal here, not the establishment of privileges that the larger community does not have.
It's our patriotic duty to demand equality for all. Historically we've had this discussion regarding women's rights, the end of slavery, and the civil rights movement in the 1960's. In each case, hindsight offers a very clear perspective that discrimination is unethical and immoral. At some point we have to embrace a true equality for all. It's about time we realized it.