This is in response to something that I thought both sad and exemplary of poor form for a Christian critic.
There are only a few very good reason for conducting public criticism of an author's work. Most important of these is to inform the public about a work that is either exemplary of Christian and literary value or utterly detrimental to a person in a profound spiritual way. Another important reason for literary criticism is to allow a reader to better understand a work. A third is to express an opinion or recommendation on a work by an established author to give the reader some indication of its worthiness for taking up an extended period of time. For private critique you may add the betterment of the author to complete the task of a writer--instruction and correction. This last is NEVER a legitimate purpose of public criticism. Such work should be conducted privately ONLY and ONLY at the request of the individual. Following Updike's rule for criticism, even if one doesn't care for a work, the exposition of it should set forth all of its best points even as one's own opinion of its merits is made manifest. But once again, this is ONLY for those well-established in the field.
Another reason NOT to pursue criticism is to show how much one knows. Or, by far the worse crime, to attempt to profit from making others look bad--either by the work of criticism itself, or by making one's own work stand out from that of the riff-raff that is not worthy to stand nearby. It is very unappealing to watch a person show off their intellectual prowess at the expense of another. If this is the way to success, it were better not to succeed.
Young writers, writers just starting out, are prone to a great many errors and a tremendous arrogance regarding the work of others. When this arrogance expresses itself in launching full tilt at T.S. Eliot, William Butler Yeats, and William Wordsworth, it can be at once amusing, and a marvelous example, as one ages of youthful folly--the literary equivalent of those pictures most mothers have of naked babies on sheepskin rugs. The folly is the author's entirely and as Yeats, Eliot, and Wordsworth are unlikely to suffer any real harm at the hands of one so arrogant as to take them on, only the author is likely to suffer any consequences.
However, when an author takes on contemporaries, and particularly contemporaries who are just beginning to emerge into the writing world, there is only one conclusion one can draw from extensive negative public criticism. That is, of course, that the critic intends to profit from this by making his or her own work look good. This is absolutely unacceptable. One becomes the John McEnroe or Bobby Fisher of the literary world. One takes what one is not entitled to and profits thereby--the very definition of theft. By calumny and hurtful speech one is set in a better light--either with respect to one's own literary writing, or by the sparkle of one's wit and intellect. It is simply better to keep one's mouth shut and continue to produce one's own good work rather than seek to profit by the destruction of another.
So, the bottom line, one should not try to excuse the literary equivalent of chewing with the mouth open, by noting that it could improve the world for literature. Arnold wasn't able to accomplish this goal, Eliot didn't do it, Wilson didn't do it. How likely is it that some 20-something literary ingenue is likely to do so? And more importantly, who really gains thereby?
No, if the strong need to help make the world a better and safer place for literary endeavors manifests itself express it in one of two ways: write those better literary works and leave the "lesser lights" alone in their gloom; or offer to share insights with the author of the works in question--then do so privately. Public display of aggressive intellect is no more appealing than PDoA. The only poor light it casts is on its perpetrator.
And, just as TSO mentioned recently at Disputations, this sort of post piques my morbid curiosity as to the subject.
But then it also makes me glad that I survived the third decade of my life without making too much of a fool of myself.
I always took your second reason as the most important reason to engage in criticism, but I also expand it: the criticism enters into the dialog, albeit in an inferior way. However, as it can become the instigation energy for a subsequent work of art, either by the critic or the artist, or a third party, it is still an important role.
I always wanted to do this with food criticism, but the newspapers always want the Consumer Reports thing: let people know if they will like it or not, which amounts to describing something as accurately as possible and then gauging it in its own milieu.
But wouldn't it have been more interesting and more fun to use a restaurant review to begin a dialog on the earthiness of the roasted beet, and to begin a Symbolist Theory of Cuisine?
I suppose it becomes obvious why I am spending more time writing about music and less about restaurants these days.