Aggressive behavior is a staple of Internet discourse, from the day the term flame-war was coined to today's trolling. It's hard to argue that aggression and argument isn't a basic part of daily life when communicating with people over the Internet. We are desensitized to the idea of someone becoming unreasonably aggressive over disagreement or disillusionment online, because it happens so often.
In my experience the level of vitriol spread through communities has been growing over time. The Internet is growing, too, and perhaps these are connected. As people are introduced to online communities, they adopt the behaviors exhibited by other users. The Linux kernel development community has been in the spotlight through tech circles and even widespread media from time to time for high-stakes flamewars between maintainers and contributors. Linus Torvalds' rants are frequently cited, often for humor, due to the sheer voracity of his statements and attacks and the fact that he is so prominently front-and-center in the tech world. New users see this behavior and are either intimidated by it, or encouraged to perpetuate it.
Sometimes Linus even brings this behavior out into the real world, as seen here expressing frustration with NVIDIA's developers.
The PC gaming community praises itself for an exclusionary solidarity movement called the "Glorious PC Master Race," which was coined from a review of The Witcher in the video series Zero Punctuation by game journalist Ben "Yahtzee" Croshaw. It would not be surprising to me that people unfamiliar with games culture might be taken aback by the simultaneous reference to the aryan master race concept associated with the Nazi party. Yahtzee's videos in and of themselves are case examples of vitriolic Internet language in the vain of media review of video games, and the PCMR niche constitutes the same behaviors exhibited to comedic effect in Zero Punctuation. However, as one can see in the following forum posts taken from the Call of Duty: Black Ops III Steam forums, it is not quite so funny:
The antagonism expressed towards anyone seen trespassing on their perfect world representation of PC players is palpable, to the point of veiled threats. A call to report players to remove them from the game is made by OP. Simply for using a game controller instead of the "preferred" keyboard and mouse. As personal anecdote, I play this game with both control schemes and I do not find a significant benefit to using either, other than by preference I choose to use the keyboard and mouse scheme.
Why is this kind of language so widespread? In short, because it's always been this way. That statement is the source of inaction for people with power to put a stop to it. The prevailing thought is that, "people on the Internet are just like this. You can't stop it, otherwise there would be nobody talking online." This is a self-fulfilling prophecy, however; antagonistic behavior prevents people who would otherwise be interested in friendly dialogue with strangers online from even attempting to speak up. By moderator inaction towards antagonism and exclusionary behavior, the attitude propagates to other community members and the consensus is made that attacking people who are not "in the know," so to speak, is acceptable behavior. It's reinforced every time someone makes a post on a forum calling out "shitty players who don't play the objective," where people with negative experiences echo the sentiment without considering the people behind the issue.
We see this in chan culture in particular: on image boards like 4chan, exhibiting behavior going against a loosely defined, ephemeral set of social norms lands you the label of "newfag," (nsfw) as an attempt to ostracize those who will not conform to their standards. It becomes a vital identity issue for members of the community to uphold their antagonistic values, otherwise facing social rejection. Since 4chan is a haven for people who've faced socialization barriers in real life, the mental consequences of rejection are magnified dramatically, and we end up seeing the rise of ideas like the "friend zone" and "normies" which in and of themselves are identity labels meant to facilitate solidarity against cultural norms outside of the community. Nobody actually believes in the idea that women are candy machines in which sex-deprived men put niceness coins into in exchange for sex, and that being put in the friend zone is a violation of that contract, I would hope.
The consequences of this are dire: as vitriol festers and is left unattended, it excludes otherwise reasonable people and makes hate a status symbol, making a downward spiral of community attitude. Any positive dialogue that may have occurred before is impossible in this environment of pervasive antagonism.
The solution is simple in concept, but difficult in execution: communities need their leadership to step up and fight against this behavior so that it does not stifle fair discourse. The resources required are, sadly, proportional to the size of the community. This means that the larger a community becomes, the harder it is for its leadership to maintain control. It is much easier to start moderation early than late, because it sets a self-enforcing standard with older members of a community, but it requires the whole community to be vigilant in its efforts to quash exclusion.
I am far from the first to identify and discuss these matters and there are people far more qualified than I to write on it. But it is the social responsibility of every person who uses the Internet to understand this problem and how it affects us. If someone came to a crowded convention hall and began shouting profanities at people whose cosplay were not quite up to their standards, they would be swiftly removed by security for disrupting the peace. If a person jumped into an innocent conversation about feminism between two adults at a restaurant and began demanding they "debate" them on the "true definition of feminism," restaurant staff would likely kick them out on the streets. Why don't we set these same standards on our Internet communities?