In "Hoist High the Roof Beam, Carpenters" [sic, see below] (the first and best of the Glass pieces [sic again]: a magic and hilarious prose-poem with an enchanting end effect of mysterious clarity), Seymour defines sentimentality as giving "to a thing more tenderness than God gives to it." This seems to me the nub of the trouble: Salinger loves the Glasses more than God loves them. He loves them too exclusively. Their invention has become a hermitage for him. He loves them to the detriment of artistic moderation.This encapsulates perfectly the feeling I've had reading so many novels where the protagonists are not even given the illusion of being free agents, but come off more like captive dears, gently manacled to their creator's infatuated view of them, lovingly force-fed bon-bons of description, the cruel world kept at bay except to maybe break a heart here and there or kill off a set of uninteresting parents. Nabokov, for example, was terrible for this, especially post-Pnin.
The author never rests from circling his creations, patting them fondly, slyly applauding. He robs the reader of the initiative upon which love must be given.
(About that goof on the title, etc., here is the letter to the editor that sets everything straight. See? Even Updike fucked up titles...)