So Hitler saw the people who destroyed German were the Jews with their superman concept
Hitler looked so far into the abyss in how to defeat them he decided to copy their methods using the Germans as the superman.
Law abiding citizen is about a man with great loss and having been corruptly cheated of Justice. He then looked so far into the abyss he killed innocents to get his revenge and caused the same suffering he had.
Nick was the devil at first and learned his lesson about taking the shortcut or cheating justice for worldly rewards. The Law abiding citizen had changed into the nick character and now is in hell with the fires.
Do not become what you hate.
Thus the extremely long process of the Q stuff to save Humanity. We have to do it right or we become what we hate.
Like the character Paul in Dune. He wanted to stop the evil Emperor but installed a horrible dictatorship that killed Billions and took away free will.