Up until recently I lived in North Carolina and I can tell you this, most Christians there have no problem with Civil Unions. The reason why this bill prohibits Civil Unions is simple:
Biblically speaking, Gay Marriage should ever be allowed however, homosexuals are very insistant that they want gay marriage or nothing at all. Civil Unions are the middle ground. By taking Civil Unions off of the table, it is a sign of strength, that if homosexuals are unwilling to negociate on this issue then neither will they. Civil Unions are the ultimate goal however, if homosexuals are not willing budge on their position of "all or nothing", then they will get exactly what they asked for... nothing.