Regarding general online comments versus giving individual private rebuke… giving tochacha needs diplomacy – “V’ohavtoh l’raiachoh komochoh”, then – “v’lo sisoh olov chait”.
Macho’oh, on the other hand, works differently. That applies to something like Chillul Hashem (i.e. saying an aveira is not an aveira or someone publicly committing an aveira, etc.), where it is not done for the sake of the individual, but for the sake of Kovod Shomayim, where dealing coolly, or even appearing as such, only intensifies the Chillul Hashem as it demonstrates a lack of empathy for Hashem’s Kovod and Kovod HaTorah.