One of the most famous lines in the gospel is “let the one who is without sin cast the first stone.” Jesus is alluding to Deuteronomy 13:9 and 17:7 (cf. Lev 24:14), from which the legal tradition of facing an accuser is based.
This verse is usually taken out of context and directed at judgmental Christians by people who are rather enjoying their sin. There is an presumption that religious leaders are stuffy, puritanical types who are out to punish other people who are committing the same sins they are doing in secret. In fairness, there is quite a bit of that sort of hypocrisy in the church. Someone like Fred Phelps has done a great deal of harm to the possibility of sharing the love and grace Jesus offers to people.
However, it is impossible for there to be no judgment of right and wrong at all. There are some behaviors which are wrong (adultery is rarely condoned by most cultures, this is more than a sexual taboo!) Usually sexual ethics are the problem. Few people have a problem called theft or murder a crime, brutality should condemned by everyone. But I am not sure I hear Christians harshly condemning financial fraud or violent crime quite the same way they do sexual sins. Did any Christians make an emotional condemnation of Bernie Madoff?
Rather than condemn people who live a lifestyle in contradiction to what we believe biblical Christianity demands, it would be better to find a way to express our belief that the behavior is sinful and that a person can be forgiven without being hateful. Telling someone they are a horrible sinner doomed for hell rarely works, and in most cases it drives people father away from the Gospel.
The saying of Jesus also is a caution for those who condemn others for their behavior. We do more good by confessing our own limitations and struggles and helping people to recover from destructive lifestyles. Christians who deny they struggle with sin create an inauthentic situation which further alienates those who need the gospel.
Jesus never denies anyone fellowship around the table because they were thieves (tax-collectors) or sinning sexually.
The common use of the phrase “cast the first stone” to silence condemnation of sin ignores the rest of the story. Jesus also tells the woman to “sin no more.” Jesus does demonstrate forgiveness and grace, but he also makes a clear statement that her behavior must change. Since her sin is self-destructive, to continue in it would be foolish.