Above all, "dirtbag" is the kind of thing people call their political opponents. And if you're powerless enough, and if you hear this kind of insult enough, what are you going to do? What all marginalized people do: you're going to wear the slur as a badge of honor.
So it says everything about Jeet Heer's latest that he can write an entire article on the insults and incivility of the Dirtbag Left - without even a mention, in passing, about how they got their name.
When an article like Heer's appears, it's tempting to respond with sneers and jeers - that is, to lay out the endless incivilities and attacks leftists endure from liberals. And they aren't hard to find; as Sam Kriss recently noted,
every single pundit or journalist who goes on a moral crusade against left-wing social-media crudery will have, very recently, done the exact same things they’re complaining against. They will have used insults, personal attacks, expletives, epithets, or unpleasant sexual suggestions; they will have engaged in bullying or spiteful little squabbles...Focus on insults and rudeness, and you will have no problem exhuming the crass hypocrisy of liberals who concern-troll about the rowdy left. But here, I want to note that if you focus on insults and rudeness, you will miss the great assault of liberalism, and an entire language of antagonism and disrespect. Account for this, and you may even begin to suspect that "dominance politics" is not a label best applied to one of the smallest political factions in the United States.
Because as it turns out, liberals (in the colloquial American sense) share with conservatives absolute power in this country; they control our politics, our economy, our culture, our institutions, our discourse, our memories of the past, and our visions of the future. And the left's true rival, liberalism in the international / philosophical sense, is even more dominant; it exercises global hegemony to a degree that is simply without historical precedent. For the socialist, liberalism is a system which subjects us to constant violence, antagonism, and degradation - and complicity in this system means complicity in all of these attacks.
It's easy for this sort of point to become lost in abstraction, so consider this specific example: lesser-evil voting.
Every two-to-four years, leftists are reminded that we have to vote for Democrats; invariably, we are told that this obligation has been imposed not by liberals, but by "the two-party system", which has cornered everyone into the lesser evil dilemma once again. And yet it is plainly true that liberals have no real interest in ending this system; there is never any serious effort by elected Democrats or by their (overwhelmingly liberal) constituents to do so. Some of them will even fight such efforts, but in general this kind of active opposition isn't at all necessary - if they want to dominate leftists, liberals can just stay at home and do nothing at all. This is how liberals tell leftists to bend the knee.
Or consider the popular liberal slurs "brocialist," "dudebro," "Bernie Bro," and so on. Confront one of the cleverer liberals about this, and they will insist that they aren't actually using this slur to misgender leftist women - they're just using it to narrowly refer to leftist men. But liberals can play coy about this precisely because media and political messaging organs have spent several years baking into our discourse the myth of a male-exclusive left; and those organs, of course, are overwhelmingly controlled by liberals. The insult to women is as crude and vicious as you will ever hear from anyone else on the political spectrum, but liberals don't have to say it out loud anymore; they can just blow the dog-whistle, and the public will hear what liberalism has taught us to hear.
These are the dominance politics of liberalism: they are far more hurtful, far more belligerent, and far more consequential for political outcomes in our world than the petty insubordination and cathartic irreverence of American socialism. Understand dirtbagism as a big fuck you to the Chaits, Tandens, and Ygelsiases who defend this imbalance of power, and Jeet's reproach about fraternity and sorority starts to sound a lot like that classic refrain: "So much for the tolerant left."
It's true: socialism is going to be aggressive in its fight for justice and equality. Liberalism, meanwhile, can play a different game - for example, it can issue constant, one-sided calls for civility across its massive industrialized media apparatus, knowing full well that only a few voices (like Chapo Trap House) will ever respond. As Stanley Fish put it, "Liberals...need not be so aggressive (although they will always be passive-aggressive) since the field, as it is presently demarcated, is already theirs."