Christians are called to judge what's right and what's wrong but they're not called to be the final judge. Now the problem is that sometimes people can get too self-righteous without realizing that there's a huge beam in their own eye while noticing the mote in the other's eye. In the Christian growth, while they're indeed called to go against sin but it's very hypocritical if they at times fail to really judge themselves first. That's why Jesus warned His followers to beware of the leaven of the Pharisees.
It's a shame really when a Christian gets rebuked by the actions of the world. You can think of the statement, "Don't even the pagans do that?" It's a shame when an unsaved person does the appropriate thing while the Christian does the inappropriate thing. That's why self-examination has been called for because Christians may not be living like the rest of the world but they're not sinlessly perfect either.