Criticizing others is a tricky act that very few are really good at. It should be as rare as the individuals who can do it well. If you must do so, try the sandwich approach. Start with one praise, then slip in one constructive suggestion, and end with words of hope and encouragement. If you feel this requires too much planning, then you probably shouldn't proceed in the first place.
Ultimately, then, the critique should truly be for the person's benefit. There are too many opportunities and things to do in life than to bring someone down and simply leave him or her there. In other words, don't waste your precious moments on such low to negative returning endeavors, especially when there are more attractive options. Anybody with no sense of direction, strategy, or leadership can destroy. It takes someone with a clear, deliberate mind to employ wisdom to everything he or she does.