Well, the first Amendment in America states:
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."

So technically, in a governmental sense, we're not -supposed- to be overly religious, but I think the number of Christians in the US ends up affecting the government and the law. It's an unfortunate little loop hole. :/ Not to mention we have a very religious president who went so far as to try to amend the constitution to ban gay marriage, which would have been in direct violation of our First Amendment. I think that's a problem, and a sign that one specific religion has a bit too much influence in this country.

I have never heard an argument against gay marriage where religion was not somehow involved. Yet it's still illegal in most of the US. Same for adoptions by gay parents. If any individual citizen is supposed to, according to our constitution, be free to believe/practice under whatever religion or lackthereof they choose, why do we have laws or bans on certain practices based solely on religious beliefs? (That's a rhetorical question, by the way, the answer's pretty self-evident).

I have no issue with people making personal choices in their lives based on their religion, or practicing their religion. But I do have a problem with my personal freedoms being affected by someone else's religion. I'm not Christian, I'm an atheist. I'm not gay, but if I were, I'd want the freedom to be able to marry the person I loved, regardless of gender. But I wouldn't be able to in most states. Why? Because someone else's religion says that it's wrong. Mine doesn't. Why should my life be affected by another religion's laws in a country that's supposed to have freedom from religious rule?