Well, fortunately the atheists don't HAVE any gods to pray to, and they really don't care who is praying, or when, or even where, with the exception of keeping the prayers out of official government meetings. Religion has no place in the American government, by law.
And we can at least agree on that, to a point. If the actual book (or flag, or icon) being burned had some historical or religious significance, such as the Gutenberg Bible, or a Torah stolen from a Synagogue, it is probably going to be considered a felony, since you are destroying property which doesn't belong to you. But in this particular case, it was a copy purchased by the group for the express purpose of being burned. While it may show disrespect for the religion, it is not destroying an historical or holy artifact.But I also believe that burning a book, like a flag or any effegy, however distasteful, is also a part of ones freedom of expression.