if u come into my house in the middle of the night and attack me with a meat cleaver, I will try my best to prevent myself from injury... if u call me a fool on a forum, I am happy enough to have evoked a response from u, and even if u slate me and resort to calling me names, I will neither hold it against u or sit at home worrying about it...I think flow has the right idea about avoiding confrontations, if that is what flow does, as ultimately, a confrontation means u attack or defend, whereas turning on ur heels and heading for the hills means u'll live to see another day... even the "saints" are "guilty" of not sticking up for their beliefs when it means death- I'm thinking of peter after the crucifixion...
as for looking away when someone commits a sin, who determines what is sin, and who decides its ur place to intervene? didnt jesus say something about those being without sin casting the first stone? there but for the grace of god goes u...
I consider: To condemn on a forum would be to censure. Casting stones would be the equivalent of deleting posts or banning people from posting. Personally I have absolutely no interest in condemning anyone, and it is also not my forum. So lets differentiate between reading someone's words and being stirred by them versus condemning someone for their words or actions.
There are maybe a few sins a person could commit over a forum. But considering all sins, realize that while there is a perpetrator (the sinner), there is also a victim of the sin. It is the victim that I would rightfully stand up for and get involved for. It could be my own judgement by the golden rule: doing for my neighbor as I would have my neighbor do for me. If I took action I would care about the perpetrator, and I do not wish to harm him/her, but I also care about the victim. So if a person commits a sin then I consider it is my duty to oppose the person by a full range of options. I have looked away before and I feel it was wrong.
If I were purely an animal in the wild as a prey, I understand there is a "Fight versus Flight" decision. The 'fight' might be throwing stones, or otherwise physically opposing the predator. The 'flight' might be running away but also to hide, evade, play dead, or outright lie, etc... It does NOT behoove either the predator or the prey to communicate with each other. Any pleas for mercy are ignored... the predator is not going to suddenly develop a conscious and feel sorry for the prey. At best the prey might call for help from others. I generally consider God's will to be the complete opposite of both "fight" and "flight". So when someone says that 'love' is the opposite of 'hate' with a focus on NOT fighting or attacking someone, I look to see if 'apathy' is not the real motivation. I find behind the apathy is a real desire to think of oneself rather than to think of others, so it is a similar motivation as those who would directly commit a sin. Consider for example the bank wants to take money from people just as bad as the robbers that come looking to take money... the robber is probably guilty of 'hatred' but a bank executive may be guilty of 'apathy' to iniquity.
So in some important ways I consider the many methods of 'flight' away from sinners to be sinful. In the bible OT, I find that sin or guilt offerings involve the people associated with the person that directly commits the sin. So if my family or neighbors commit a sin it is as if I committed a sin too. I suggest that a person can also be guilty for what a person does NOT do. Consider in the parable from Jesus of the separation of goats and sheep that in the judgement of heaven or hell it appears that the wide and easy path is for those who did NOT do something for others. So I consider the apathetic response to sin is also a crime. I realize the focus is on not throwing stones at an alledged perpetrator, but what of disregarding the victim? Of future victims? I also know of no way to help any perpetrator or sinner except to personally get involved.
I think there is a lot of apathy in the world for a number of reasons. There is a reliance on government, the lawmakers, police, and courts to instill social order. So should people put down the judgement and condemnation the government provides the people as a service, while also benefitting from it? I don't know about throwing stones, but a fair number of people are living in prisons. Many were apprehended by force using weapons. Are the police or judges the cause of increasing hatred in the world? Should they be avoiding conflict and controversy? I say NO. They are public servants. I only think government needs to be under a far tigher grip of the people, each individual. I submit that the making of laws, which determines what a SIN is, needs to be more distributed among the individuals of any group of people. I think the right way forward with government is to seek far greater representation by direct democracy. Quite simply, "No taxation without representation". So to answer your question of who determines what a SIN is... I submit that it needs to be everyone. Surely as a result there will be controversy.