All perfect praise be to Allah, The Lord of The Worlds, and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
It is obligatory for a Muslim who hears or sees an evil to disapprove of it to the extent of his/her ability since the Messenger of Allah(PBUH) said: " Whosoever of you sees an evil, let him change it with his hand; and if he is not able to do so, then [let him change it] with his tongue; and if he is not able to do so, then with his heart—and that is the weakest of faith.” [Muslim]. This legal obligation protects the community against corrupt behavior, and makes its members more responsible.
Nonetheless, it is bound by legal rules and conditions to protect people`s privacy and freedom as well as to stop dispute from spreading among them. One of the rules that scholars have stated in this regard is: "The evil that must be changed is the one considered forbidden by consensus of the scholars; whereas, it isn`t permissible to change the evil upon which scholars have disagreed; rather, it should be discussed in ways that are best and most gracious. And Allah Knows Best.