Constructive criticism is good it helps the individual to know his or her strength and what is lacking. When you criticize someone constructively, the person appreciate it and in turn, tries to be a better person.

Destructive criticism on the other hand destroy the persons ability to improve, it makes one feel less of himself and in turn, the desire to be a better person will vanish. The bottom line is, we should always try to criticize each other it's love.