I am a member of the Lord's church. Would, or could, the sin of viewing pornography be considered a public sin if the person who was guilty was another gospel preacher who had done so over the entire period he served at his congregation, and others in that congregation, as well as others in another congregation, and several outside the church knew about it?
I also want to personally thank you for the excellent work being accomplished through your website! I have searched for several articles as of late on various topics that do not seem to be discussed within the brotherhood, but it always seems like I get several hits referring to your site on these same subjects. This is greatly appreciated! Many thanks!
Any sin is public when multiple people are aware that the sin took place. When trying to get a person out of sin, the goal is to limit who knows about the sin to the minimum necessary to get the person to change. This is seen in Matthew 18:15-17. It is also what is meant by "covering sin." It isn't the hiding of a sinner in his sins, but a burying of past forgiven sins. "Brethren, if anyone among you wanders from the truth, and someone turns him back, let him know that he who turns a sinner from the error of his way will save a soul from death and cover a multitude of sins" (James 5:19-20).
Sometimes you will find people who claim that a public sin requires a public confession; however, this requirement is not found in the Scriptures. For details see: Does sin require a public confession before a congregation? and Doesn't a publicly known sin need to be confessed?