As a follow up, I'd like to quote an excerpt from an article that addresses that very same topic:
Society only tolerates sexual sins and sins against life. And that tolerance is strictly enforced. People trudge out the “do not judge” phrase and use it like a club to silence anyone who might speak against such license. People trudge out the “do not judge” phrase and use it like a club to silence anyone who might speak against such license. Society also rewards anyone who abides by its rules and strikes the word “sin” from his or her vocabulary. Christians are just as susceptible to wanting to be liked as anyone else.
A pillar of holiness according to St. Francis de Sales, is hatred; hatred of all that is evil, hatred of all that God hates. We know “what” God loves. God loves us unfathomably! He created us in His image. He suffered the most painful death in human history to save us from our sins. He dwells intimately within us in His Holy Spirit. But God does not force us to love Him. He would never have had it that way. There is always that chance we will pick sin over His love and He will lose us forever. So, what does God hate? Sin! He hates sin in the same way a mother hates the cancer that is devouring her precious child. The way a father hates the drug addiction that is destroying his son. God hates sin because it kills us. And if we love God and are our brother’s keepers, we should hate it too!
That is why we need to judge.