my answer was phrased in the form of a question.
deal with it.
Clearly, you consider new testament authors infallible, except when you don't, of course.
Rubbish.
You give an example of something that was never considered a sin becoming unjustified in the secular social contract, while he speaks of something that is directly referred to as sinful being justified because of the same secular judgment.
What was sinful is still sinful according to what Jesus said about the New Covenant.
Even people who are not Christians, such as myself, can see the difference here.
Making something that isn't sinful against the social contract would cause Christ to say, "Follow the law" which he, and other authors, said often. Attempting to make something less sinful because man says it is okay per the contract, well Christ spoke to that as well with much less agreement. Secular laws, or social contracts, do not make something 'not sin'. While they can make something that was acceptable in one time, unacceptable in more current times.
While I disagree with the sentiment of 'sin' in these cases. (My beliefs tell me that as long as they harm no other, sacrifice none other than themselves, and do not seek to harm those they love they are well within what is Right.) However, if you believe what is said in a book to be the Word of God, then it becomes something significantly different.
Are you saying that the book is not the Word of God?