In America, usually freedom of speech is the basic law of what can be said. That means that I can say what I want to you, even if it's hurtful, even if I do it TO hurt you, no matter what. Message is message. The reason this works so well from a legal perspective is because trying to put law around what can be said becomes so murky and ripe for abuse.
However, the fact is, words often can hurt more than physical violence. So instead we have norms around what messages are appropriate. Certain words are "off limits" in most settings "Nigger, Cunt, Retard" and people will socially shun you if you use them with negative intent. However, again, this becomes murky and ripe for abuse, think of those who keep playing the "you're a racist" card as a political tactic. (https://en.wikipedia.org/wiki/Controversies_about_the_word_%...)
So those people who have been the victim of politics (you used a gender-specific pronoun, now I will shun you, but I'm really doing it because I don't like you and want to hurt you but have a convenient social excuse to ostracize you and look like the good guy for doing it) often overreact and take out their anger anonymously online.
I bring this up because. I think once both groups understand each other, this entire quarrel will start to subside. Those who don't even try to understand the other side I can only assume want the quarrel to continue.