Christ Himself spoke on these matters, condemning men who even look lustfully at a woman as adulterers.  That is a pretty high standard!  And, just because a majority of people reject a teaching, that does not mean that the teaching is either false or invalid.  Remember that the VAST majority of people in Galilee and Judea rejected Jesus and His teaching, and that, even today, more people globally are not Christian; therefore, using your logic, that means that His Gospel is false and invalid.  

Peter denied Jesus, Thomas doubted Him.  All but John ran away in cowardice when He was arrested and crucified.  By the logic of your comment, because of their history in this, the Apostles should have "shut up" on all matters of the Gospel.  Yet, thanks be to God that His grace, and His Spirit, made up in them what was lacking, just as He does in the Church today, just as He does in each of us.

If the Bishops ceased preaching the Gospel in full, it would be a sin of omission.