"...the average reader knows poetry mainly from anthologies, just as he knows philosophy mainly from histories of philosophy or textbooks: the Complete Someone--hundreds or thousands of small-type, double-column pages of poetry, without one informing repentant sentence of ordinary prose--evokes from him a start of that savage and unreasoning timidity, the horror vacui, with which he stares at the lemmas and corollaries of Spinoza's Ethics. Those cultural entrepreneurs, the anthologists, have become figures of melancholy and deciding importance for the average reader of poetry, a man of great scope and little grasp, who still knows what he likes--in the anthologies."Personally, I think anthologies are to poetry what radio is to music. They're a good way of checking out what's out there, and catching the new voice or two that you haven't heard before, but if they're all you read then you're not really interested in poetry.
Of course, there are anthologies and there are anthologies, and it's useful to distinguish between them. Off the top of my head, I can think of at least three reasonably distinct types (though admittedly the line between them can get blurred): anthologies of 'new' poetry (Best American Poetry), anthologies of poetry from a particular region / language (The Book of Japanese Verse), and 'theme anthologies' (100 poems about horses) or anthologies that recycle the canon in cutesy ways (100 best-loved poems of all time). The last one of these I dislike as well, but the first two can be useful.
Where Jarrell's wrong, I think, is in his assumption that the anthology is a way of coping with massive volumes of poetry by a single author. For me personally (I probably read about three or four anthologies every year), the anthology is more a way of coping with the endless volume of new poetry that gets published every year, as well as the almost infinite wealth of poetry that exists in languages other than English. Obviously, the filter of an anthology means that this work loses much of its flavor, so that reading anthologies is an imperfect way of becoming acquainted with it, but it's better than not getting to know it at all, and probably better than whatever haphazard sampling of it I could manage on my own. Without Paterson and Simic's New British Poetry, for instance, it would probably have taken me a lot longer to discover Sean O'Brien and Gwyneth Lewis - not because I wouldn't have heard of them, but because the chance that I would have gone to the library and issued out their books without having read (and enjoyed) half a dozen of their poems first is incredibly low.
Not, of course, that anthologies are the only way of expanding your poetic horizons. Literary journals are another way of getting to know new work, but there's such a bewildering variety of those, that you've got almost the same problem there that you do with books themselves. Blogs and poetry websites are useful as well, and I can see the argument for them eventually substituting for the anthology role, but that doesn't mean anthologies aren't valuable in their own right.
In the meantime, the problem is not so much with anthologies per se, but with the potential decision of a reader to restrict himself / herself only to anthologies. If the only poetry you read is in anthologies, or if you stop your exploration of a particular set of poets with their anthologized work, you're missing out on a lot. But there's no reason why, as readers, we have to stop there. The fault, then, is not in our books - it lies with us.