Question to Shaikhul-Islaam Ibn Baaz, rahimahullaah:

Is it permissible to mention peoples’ names and characters when one wants to criticize them and their thinking?

Answer:

If someone writes something that contradicts the pure Shari’ah, and distributes that material, or if he promulgates that view in the media, it becomes compulsory to refute him and expose the falsehood of what he says. There is nothing wrong in mentioning that person’s name or in warning people about him if he calls to innovation, Shirk, or if he calls people to what Allaah has prohibited or to disobedience. Until this day, there are knowledgeable and believing people from the callers to the truth and bearers of the Shari’ah fulfilling this obligation, sincerely for Allaah Almighty and for the benefit of His servants, rebuking the wrong, inviting to the truth, warning others against those who propagate falsehood and destructive rhetoric.

Shaykh `Abdul-`Azeez Bin Baz 
Fatawa Islamiyah vol.8, p.53.