Though the task of admonishing another believer is not pleasant, it is necessary. The Bible commands us to do it and the price of not doing it is high. What is at stake is their very salvation. What is at stake is forgiveness. What is at stake is a life that is pleasing to God.
Nothing can be more cruel than to leave someone in their sin.
And, nothing can be more compassionate and loving than to call a sister or brother back from the path of sin. If you truly love and care for someone than you take them aside and point out the error of their life or doctrine or job performance so that they can live a God and Christ-glorifying life. When you rebuke someone out of love and with compassion and humility they usually sense that you are willing to risk rejection and broken relationships for their good. They will come to the conclusion that what you are practicing is tough love. Eventually they will reach the point where they will thank you for your love.