What constitutes “heresy” and “orthodoxy”?

Does acceptance of same-sex marriage on the part of a Christian constitute “heresy”?  It may be wrong and un-Biblical, but does it rise to that level?  Conversely, can a Christian hold other-than-traditional opinions on sexual morality or other issues and still be considered “orthodox”? Calvin College professor James K. A. Smith has ignited a controversy over the definitions […]