Correction: this was not a case of accidental misgendering. The post refers to someone abusing mod privileges to edit someone's pronouns to "who/cares".
Hate and intolerance could be one reason, but there are others. Ignorance, immaturity, prejudice and steoreotyping, etc.
And the way to deal with that is through compassion. A good start is to feel sorry for them.
Those are all signs of a toxic community, which is what this article is about
That mod is likely an ill-intentioned guy and in violation of the Discord ToS, but starting every conversation by accusing others of being ill-intentioned is how we end achieving nothing as a society.
Punishment and an escalation of intolerance are not the goal, tolerance is. We are not going to heal the world one accusation or insult at a time.
When you are not a prejudiced person, a good starting point is to consider yourself fortunate in that respect, and then acknowledging others might not have been as fortunate as you.