Let's start with "authorial intent"
This is a much misunderstood and abused term, and I think some people might be misunderstanding it on purpose. It's a familiar term in critical discourse, and I don't know why it needs to be explained, but apparently it does. It has a specific meaning that has nothing to do with magically "knowing" what the artist was "trying to do" like some are claiming. That's just a red herring. That's not what it means at all.
Poetry is more than mere building blocks; it's communication, and all communication has a purpose, which to say it has intent. In critical discourse, engaging with "intent" has more to do with understanding how the poetry works within its given mode, understanding how a text has been assembled and reading it with an eye towards understanding its purpose, its message, and its content. For example, one would not (should not) measure a poem by E.E. Cummings with the same material yardstick one would use to measure a poem by Robert Frost, or whichever two dissimilar poets you might choose. The two poets have a different ethos, a different project, a different way of communicating, a different "intent" that is expressly manifest in their work.
It's disingenuous to say a critic cannot, given a close reading, determine the functionality of a text, and from that, extrapolate its purpose and gauge that against the traditions it either draws upon or tries to subvert. It would be an incompetent critic indeed who could not do that, but that is what it means to engage with the "intent" of a text in critical discourse. It has nothing to with reading the author's mind. If a critic understands the "intent" of a piece, for instance, he will not declare that a poem failed to be a sonnet when in fact it meant to be a lipogram, or vice versa.
Different modes of criticism have their own relationships with the idea of authorial intent: deconstructionists, post-structuralists, materialists, etc. Only the most rigidly fundamentalist critical approaches disregard "intent" completely. In doing so, they create large black holes in the reading of a text. They miss the point on purpose, so to speak. I dislike fundamentalisms of any kind, and that includes both critical and aesthetic ones. In poetics, at both the conservative and radical ends of the spectrum, you have those modes that fetishize their own kind of formalism to the detriment of (or even to the exclusion of) concerns about content. At either extreme these formalist fundamentalisms (say a revived take on the radical poetics of Oulipo or an orthodox approach to classicist meter and rhyme) you will find a kind of literary tunnel vision; the poems are toying with their physical minutiae, but they are disinterested in actually communicating much of anything. When such fundamentalists bring their aesthetic ideology (their dogma?) into the critical arena, they end up measuring poetries against it that aren't compatible with their criteria. Holders of this position cannot help but commit the fallacy of saying, "the non-traditional is bad because it is not the traditional" or vice versa. They mistake the rationalization or the justification of taste with the application of reason and critical rigor. They are, in a sense, defending a camp. They are saying: I have staked my poetic identity to this ideal, and now I must protect it and evangelize it. But creativity isn't fostered by defending a camp. It comes from exploring strange, new lands. The plural and open are fruitful, while the limited and the closed are doomed.
And what does this have to do with "snark"?
Quite a lot, actually.
But first, let's remind ourselves exactly what "snark" means in terms of book reviewing. The term was coined by Heidi Julavits in an essay in the March 2003 issue of The Believer magazine:
I fear that book reviews are just an opportunity for a critic to strive for humor, and to appear funny and smart and a little bit bitchy, without attempting to espouse any higher ideals—or even to try to understand, on a very localized level, what a certain book is trying to do [italics mine], even if it does it badly. This is wit for wit’s sake—or, hostility for hostility’s sake. This hostile, knowing, bitter tone of contempt is, I suspect, a bastard offspring of Orwell’s flea-weighers. I call it Snark, and it has crept with alarming speed into the reviewing community... (link)
So, according to Julavits, a refusal to engage with intent is a key ingredient in snarkiness. The critic is there to look clever and bitchy, and engagement with the books, and with literature in general, is secondary. Snarkiness is inherently self-serving, and generally at someone else’s expense. It’s selfish. I agree that this style of book reviewing has become all too prevalent in recent years. I believe that even if a reviewer dislikes a work, he can afford its author the dignity of treating it seriously, and if he does not believe a work warrants serious critical attention, positive or negative, then why review it? Just to be bitchy?
This raises another issue. Whenever the issue of snark or nastiness in reviewing is raised, someone, usually the offender, inevitably cries, "What? You don't believe in negative reviews?" Again, this is a simple case of missing the point on purpose. A bitchy tone and a critical value judgment are not the same thing. A snarky book reviewer is no more a “critic” than a muckraker like Perez Hilton is a “journalist.” A reviewer can offer a negative value judgment without being snarky, entertaining himself with his own barbs. Indeed, such a rancorous tone can be evidence of an ad hominem fallacy; if a reviewer's tone (or, indeed, his language) suggests that he believes the author is inept (rather than the text insufficient), then he is guilty of an ad hominem fallacy. This seems to go hand in hand with the fallacy that all insults are honest and all civility is phony, or that trying to hurt or demoralize people is a valid critical stance.