The impatience with which many writers (and some critics) regard "negative" reviews is in part a natural enough response, reflecting the tense relationship between artists and their critics that has probably always existed. On the other hand, it seems to me that such tension has become particularly acute in our time because of two simultaneous and seemingly contradictory phenomena: There are more published and aspiring-to-be published writers than ever before, and the audience for serious fiction (and poetry) continues to diminish. In these circumstances, negative reviews threaten to undermine the "community" that has come to substitute for the cultural recognition poets and novelists have lost and might deprive writers of whatever small chance they have of gaining readers among what remains of a general reading audience.
Defenders of negative reviews often justify them as providing a service to readers, who will be cautioned against spending their time with an inferior book. Even those who don't think reviews are primarily a form of consumer guidance (and thus a function of capitalism more than literature) nevertheless generally contend that the evaluative role of criticism should take precedence, helping readers come to a conclusion about a given work's merit. If this is done by offering evidence and cogent analysis, it is a perfectly valid exercise, although it would seem that the occasions for performing it should be limited: What's the point of subjecting a book by an early-career writer to harsh critical treatment when it's not likely to attract much of an audience anyway and can safely be left to its fated lack of attention as an ultimate verdict? Why take up too much review space and critical effort with bad books when what's really needed is for the good but neglected books to be discovered?
After all, in the long run lengthier critical commentary isn't going to be afforded to truly inferior work. Literary criticism of a more extended sort almost always centers on books that have continued to resonate, whose success is no longer at issue. Few serious critics--and not just academic critics--are going to devote these opportunities for more thorough critical reading to largely superfluous evaluation. Despite the widespread impression of critics as prescriptive taskmasters, literary hanging judges, evaluation is not the most essential task taken up by the literary critic. At their best, critics are not judges, but more like witnesses offering an account of the reading experience that has a tentative authority that comes from close and conscientious reading allied with a grasp of context--literary, cultural, historical. A critic of this kind describes, makes connections, explicates, albeit as the means to the discovery of value, a discovery the critic hopes the reader will share.
If criticism is not the act of rendering a critical verdict on a literary work, neither is it any kind of evaluation of the author of the work, a divining of the author's character or moral standing from his/her "presence" in the text. Thus a negative review is not an attempt to find fault with the writer but to point out flaws in the work through identifiable standards. (If the standards can't be identified then the review itself is fatally flawed and can't be taken seriously, anyway.) Likewise, a positive review is not an affirmation of the writer, but the qualities of the book at hand that make it artistically successful. Quite likely most writers would not take such offense at negative reviews if they didn't implicitly believe that a positive review is not just an expression of approval of a particular book they've written but also approval of their decision to be a writer, an acknowledgment of their inherent talent.
In my view, most of the debate about positive and negative reviews is misguided not only because it oversimplifies but because it proceeds according to mistaken assumptions about the objective of reviews, and of criticism in general. Reviews should not be written as a kindness to either readers or writers but as a contribution to the continued relevance and vitality of literature. While many reviews may be no more than a transitory register of unreflective opinion or superficial pronouncement (at times no more than perfunctory plot summary), others offer genuine insight into the immediate context and the aesthetic effect of the book under review, and the very best also help maintain the continuity of literature by declining to write about a new book as if it has arrived shorn of all connection to the writer's other work and to important literary history. Collectively, reviews provide the first layer of commentary on a literary work, which can be very influential in stimulating subsequent critical consideration of that work.
A reviewer can't be sure, of course, that the work being reviewed will receive subsequent critical attention. The presumption probably should be that it won't. However, the reviewer should also presume that a book presenting itself as a serious literary work deserves to be regarded as such, but also needs to be honestly assessed when it falls short of its ambition. Ultimately both readers and writers can only benefit from this kind of effort when carried out in good faith, even if it is not directly made on behalf of the well-being or convenience of either.