At present, a vaguely spiritual secularism is the dominant religion in the United States. There's room for spiritual and religious beliefs in this system, as long as they are kept completely and utterly personal and without any public expression. You can read your Bible, just not in school. You can have your faith, just not bother anyone else with it. You can believe God has spoken, but not pass laws or execute policy influenced by that belief, according to the new secularism.
In the process, that can begin to erode other liberties. If you tell someone they cannot sing Christmas carols at school because they contain any vaguest reference to Christmas, Gaia forbid, that begins to encroach upon liberty for the sake of your faith system. If you tell someone they cannot wish others a "merry Christmas" or lose their job, again, you've begun to enforce your faith system on them and damaged their liberty.