There is no reason necessary for you should not build it up! No reason why you shouldn't stop breaking things down. By things I mean relationships, projects, people, confidence, trust, faith and everything else. Let me explain.
As children we all try and make things. We are very creative and constructive. As we grow up we start to realize the joy in destroying as a part of play, stories and things around us and as negativity creeps in us, it starts making us destructive in life too. With too many negative things around we are subconsciously made to believe it is normal to destroy and it creeps into our daily life. While this is usually a phase and many of us grow out of this brat phase, some still stick around there and refuse to grow up.
We all encounter negative people in life. People who are selfish, downright destructive and so self obsessed that they refuse to see merit in anything other than what suits them. Even if there is a small win in their life they project it as the biggest achievement possible but at the same time don't think twice to strike down others. I really don't know what they get out of it. I am sure you would have encountered these kinds of people in your family, at workplace and society.
Another species of people are those who look at every possible chance to be negative. If there is a chance to ruin anything, trust them they will definitely ruin it. For some reason these people carry a lot of negative energy in them. I know quite a few people of this kind. One of the top executives in a CMM Level V company screams at his team mates in front of all the staff for the smallest of mistakes and slip ups. Another well educated guy shouted at his wife for not taking care of the child in a party full of friends and family. A guy I know passes such sarcastic sexist remarks for everything in front of his colleagues and family but because of his age people don't say anything to him. Why are some of us so negative? We speak from what our hearts are filled with.
We need to be positive. Be constructive. Be helpful. Be kind. Be the one who spreads the joy and comfort. Be the builder. Be the one who helps others grow not hurtful, sadistic, irritating, arrogant and downright bad. When you encounter such a person, remember to stand up. Make it a point that you discuss this either in person or as a group. But speak up and clarify that you don't appreciate this kind of behaviour. If they persist, chose to ignore and move on if not complain to the respective authorities. Many of the organizations have strict policies against harassment. Use them. If it still persists, seek help.
If you are one of those people who find negativity in everything, it is time to change. Time to grow up. Time to turn your life around. There is still hope. Seek help or just stop behaving the bully you can be and see how much more people will love you and bring positivism to your life. Let us be people who build it up!