One of the most famous lines in the gospel is “let him who is without sin cast the first stone.” He is alluding to reference 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 shrilly condemn people who live a lifestyle in contradiction to what we believe biblical Christianity would accept, 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.
The saying of Jesus also is a caution for those who condemn others for their behavior. We will do more good by confessing our own limitations and struggles and helping people to recover from destructive lifestyles To deny that we struggle with similar sins creates an inauthentic situation which further alienates those who need the gospel. I cannot remember Jesus denying anyone fellowship around the table because they were thieves (tax-collectors) or sinning sexually.
The common use of this line to silence the condemnation of sin ignores the rest of the story – Jesus also tells the woman to “sin no more.” There is forgiveness and grace, but there is also a clear statement than her behavior must change. The sin is self destructive, to continue in it would be foolish.