Blessed are they which are persecuted for righteousness' sake: for theirs is the kingdom of heaven. Blessed are ye, when men shall revile you, and persecute you, and shall say all manner of evil against you falsely, for my sake. Rejoice, and be exceeding glad: for great is your reward in heaven: for so persecuted they the prophets which were before you. (Matthew 5:10-12 KJV) This speaks of the righteousness of being slammed by antiChristians. But it doesn't say a bit about how denouncing that bigotry is itself SINFUL.
Words are not SWords. I can turn the other cheek to their attacks (both physical and verbal) and not physically strike back and STILL speak out against it.
What is the sin?