Because it’s a subliminal argument. Or an aspirational one. Or at least flippancy is. Or, well, wait:
Imagine a spectrum lying across the ways we communicate. One end represents being flippant, funny, referential, snarky, and concise—zingers and one-liners and sarcasm. The other end represents being earnest, thorough, measured, charitable, and serious. The difference between these things isn’t just formality, or good faith versus snideness; it’s the assumptions you’re making of the people you’re talking to. Flippancy works best for people who already agree with you in principle. Jokes and references have to be gotten; irony and sarcasm need to be picked up. They’re fun when they’re for you. The earnest, thorough stuff, on the other hand, has to waste its fun doing the boring work of reaching out to all possible listeners—explaining where it’s coming from, inserting caveats, acknowledging exceptions and counter-arguments, etc. It builds a case; flippancy gets to just dance entertainingly on a case. One is the way you talk to people who get you, the other is the way you explain yourself to people who don’t. Teenagers are really amazing at one and often really poor at the other; they like being gotten, and they haven’t collected much information yet about what other people’s assumptions even are.
So you might have been forgiven, back in the early days of the internet, for assuming the medium would encourage the earnest-and-thorough method of communication. This is, after all, a tool that allows you to post up your speech for anyone on the planet to look at; it’s the whole logical extreme of a big crowd you don’t know. And you’d have sounded right for a while, after which you’d have sounded embarrassingly dead wrong. The internet’s encouraged the opposite; it’s raised flippancy and reference and concise snarky zingers to whole new levels of sophistication, and it winds up using them like subcultures have always used inside knowledge and slang—to draw lines between audiences. (“Lady, if you have to ask, you’ll never know.”) This serves a really vital purpose on the internet, which lacks all the cues the physical world uses to tell people where they’re standing and who they’re talking to: geography and age and dress and all that jazz. On the internet there’s just rhetoric and visual rhetoric on a screen, and the more assumptions that stuff makes of its audience, about what they’ll expect and agree with and what they’ll get, the more effectively it draws a line between who’s really hearing its speech and who’s merely overhearing it—between who knows and who has to ask.
Flippancy is more fun. The work of reaching out and explaining things is potentially dull and time-wasting; it’s just plain funnier and more exciting and more gratifying to be on the inside of shared assumptions. (We like talking to friends, not strangers.) The histories of a lot of message boards and comments boxes can be traced out along these lines: they begin with a few people earnestly explaining themselves to one another, finding common assumptions and common ground and welcoming newcomers; then they grow, and their shared assumptions solidify, and they get flip and concise and referential and giggle at newcomers who stumble in and Have to Ask.
And if flippancy is more fun then it’s also more attractive. Much like the coolest kid in middle school, it’s funny and it’s exclusive and it’s confident of being understood by just the right people—maybe even especially when it’s being superior and snarky and speaking at someone else’s expense. It can be so attractive, in fact, that you want to share its assumptions, whatever they are. It’s not addressing those assumptions, or earnestly explaining them to you in some dull droning unfunny voice, but you want to share them even more, because you aspire to be on the right side of the cool person’s joke. You might not even think about those assumptions, or notice yourself adopting them.
Which means flippancy and snark can be convincing, substantively convincing, without even making an argument. They convince socially, not rhetorically. Being convinced socially isn’t anything complicated or new, not in the least; what’s impressive is how effectively the internet has picked it up in a world where there shouldn’t, technically, even be much of a “socially”—how we’ve learned to encode it in the words themselves. It can’t usually go very far; usually it offers nothing to those who aren’t very, very close to assumptions; often it looks pointless and sick to everyone else. It is quite possibly a really bad thing and a really bad habit. But you can’t say it doesn’t, for better or worse, get very real work done.