The kitchen was a shambles of broken glass and china. The dining-room was stripped of parquet, the skirting was up, the door had been taken off its hinges, and the destroyers had moved up a floor. Streaks of light came in through the closed shutters where they worked with the seriousness of creators - and destruction after all is a form of creation. A kind of imagination had seen this house as it had now become.".
The Second World War had just finished and the boys were living in a hostile and indifferent world. They had had an idea, a dream, and using their imagination the gang had created a plan (p.176 "a wild invention") to destroy Old Misery's house. To accomplish their mission they needed energy, hard work and organisation, just like in a war. However, they weren't doing it for hate, because hate requires a certain degree of passion and each and every one of them was cold-minded, and just followed the orders of their leader: Trevor, who was a mastermind of evil.
It's clear that the gang wanted prestige, distinction and fame (p.174 "The fame [ ] been destroyed"); nevertheless it wasn't just for that; they were doing it naturally and consciously and most significant: for fun. Destruction was part of them, maybe because they were "the sons of war" and they were living a period of transition when many important changes take place; but as far as I"m concerned, proportional episodes (with proportional consequences) happen nowadays. This leads me to think that "destruction" is part of human nature. .
Regarding their action, when the house was being smashed, sounds of carpentry were heard (creation) (e.g.: a clickety-clack, a bang bang, a scraping, a creaking ). The boys created destruction and they had to do it in a way so that nothing "build inside again was more beautifully than before". "Beauty", style and elegance was something they couldn't allow. The question is why; as I said before, "destruction" could be taken as part of human nature, but perhaps this is always needed to create later.