"If he cannot in good conscience obey his civic duty, he must perforce resign office"
Why isn't it his civic duty (a crafty way to phrase it)to do as he sees right? The source of a mans morality and belief does not disqualify him from participation in government. Democratic structurs give people recourse when they disagree with the law. When they do not then they are totalitarian.
This is too easy. Because that's not the oath he took!! The oath is to uphold the law, not just to uphold the laws he thinks are OK.