Here in the U.S., we are supposed to have the right to free expression. Of course, this does not mean that courts have not wrestled with how to define this and what limits should apply. As tempting as it is to argue that the right to free expression should be absolute and unrestricted, I suspect that most of us would agree to certain limitations.
If not, I invite you to imagine a 40 year-old pedophile graphically describing his sexual fantasies to your 6 year-old. I suspect this is something you would favor preventing even though doing so would involve limiting his free speech. But as clear as some of the extreme scenarios are, the issue as a whole is quite muddy.
Most atheists I have known would agree that no adult has the right not to be offended. I may not enjoy the experience of being threatened with hell when I am grocery shopping here in Mississippi, but I recognize that if I called the police to report such an encounter, they would be powerless to act. I also recognize that if I responded to such a verbal harangue by slugging the annoying Christian, I would be the one who would be punished. As an adult, this is just something with which I must cope.
In the same way, Christians have no right not to be offended. If they vandalize a legally erected atheist billboard because they do not agree with its message, they are the ones breaking the law. If hearing me say I do not believe in their god offends them, tough. If they assault me for expressing myself, they are the ones deserving of punishment.
The society in which you and I live is not some big playground policed by school officials who must worry about overly sensitive parents. As grown ups, we are expected to have developed reasonably thicker skin than our children. This is part of the problem I have with political correctness. So when someone tells me that I have no place in America because I do not share their god belief, it does me little good to tattle to someone. Bigotry like this is disappointing, but it is not illegal. And I'd certainly prefer it to remain that way.
One of the things our right to free expression confers is the freedom to insult. It is a freedom we would be wise to use selectively, as exercising it may have unwanted repercussions on our reputations, standing in the community, emotional well being, and the like. But it is nevertheless one of the ways in which we should remain free to express ourselves.