Meaning of Mischief

In his Tafsir, As-Suddi said that Ibn `Abbas and Ibn Mas`ud commented,

وَإِذَا قِيلَ لَهُمْ لاَ تُفْسِدُواْ فِى الأَرْضِ قَالُواْ إِنَّمَا نَحْنُ مُصْلِحُونَ

The fourth and the fifth verses expose the sophistry of the hypocrites -their activities threatened to produce a general chaos and disorder, and yet, in their mealy-mouthed way, they pretended to be men of good will and to be serving the cause of peace and order. The Holy Qur'an makes it clear that oral claims alone do not decide the question whether one is working for order or disorder, for what thief would call himself a thief? It depends on what one does, not on what one says. If a man's activities do result in mischief, he will be called a mischief-maker, even if he had no such intention.

Who are reformers and mischief-makers