We are continually reminded in the Quran to use our reason, guided by its teachings which we must use to judge what is going on in this world and expose falsehood wherever we find it, no matter who feels insulted or aggrieved that we are condemning a fellow “muslim” [whatever that means to them].
17:80 Say, “My Lord! Admit me in honour and let me depart in honour at every juncture of my life, and help me with strong support.”
17:81 (Time has come for you to) say, "The truth has come to light, and falsehood has withered away. For, falsehood is bound to wither away."
To answer your “I wonder how the Qur'an could be insufficient for us!”:-
62:5 (The Book of God is to be read and understood, and not placed in high niches.) The example of those who were entrusted with Torah, and did not apply it in their daily lives, is that of the donkey that carries a load of books. Evil is the example of people who deny God’s revelations by their misdeeds. God does not guide people who choose to do wrong (and displace the revelation from its rightful status).
[Kizb = Belie = Give lie = Deny in practice. Kufr = Reject openly = Darkness = Denial = Ingratitude = Concealing. Zulm = Dislodge from the rightful place = Relegate the truth = Give preference to conjecture = Oppression = Wrongdoing = Violation of human rights]