In the United States, ml, we maintain separation of church and state in accordance with our precious constitution. In a free, democratic, and tolerant American society, any man or woman including Dr. Ehrman may choose to be or not to be a Christian, Muslim, Jew, Buddhist, or whatever else he decides.
Dr. Ehrman's decision to no longer have his mind and freewill controlled by Christian Fundamentalist teachers and their intolerant interpretation of the bible does not make him anything less in the eyes of U.S. law.
And it appears that he learned more about what it means to be Christian during his biblical and theological studies at Wheaton College and his Master of Divinity and Ph.D. at Princeton Theological Seminary. http://www.explorefaith.org/bio/ehrman.html
Constitution of the United States, Amendment I
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.http://www.law.emory.edu/FEDERAL/usconst.html