They, too, can read and write, of course, but their  solecisms,   barbarisms,  and  vulgarisms  call for rebuke, and what better rebuke than to treat them as if they did not belong at all'to condemn them figuratively to the outer darkness of the unlettered?
( They ( , ( too ( , ( ( can ( ( ( ( read and ) write ) ( , ( ( of course ) , ) ) ) ( ( ( ( ( but ( ( ( ( ( ( their solecisms ) , ) barbarisms ) , ) and ) vulgarisms ) ) ( call ( for rebuke ) ) ) , ) and ) ( what ( better ( rebuke ( than ( to ( ( treat them ) ( as ( if ( they ( ( did not ) ( belong ( at ( ( all ` ) ( to ( ( condemn them ) ( figuratively ( to ( ( the ( outer darkness ) ) ( of ( the unlettered ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ? ) ) ) ) )
(ROOT (S (NP (PRP They)) (, ,) (ADVP (RB too)) (, ,) (VP (MD can) (VP (VB read) (CC and) (VB write) (PRN (, ,) (PP (IN of) (NP (NN course))) (, ,)) (SBAR (SBAR (S (NP (CC but) (NP (PRP$ their) (NNS solecisms)) (, ,) (NP (NNS barbarisms)) (, ,) (CC and) (NP (NNS vulgarisms))) (VP (VBP call) (PP (IN for) (NP (NN rebuke)))))) (, ,) (CC and) (SBAR (WHNP (WP what)) (S (ADVP (RB better)) (VP (VBP rebuke) (SBAR (IN than) (S (VP (TO to) (VP (VB treat) (NP (PRP them)) (SBAR (RB as) (IN if) (S (NP (PRP they)) (VP (VBD did) (RB not) (VP (VB belong) (PP (IN at) (NP (NP (DT all)) (`` `) (S (VP (TO to) (VP (VB condemn) (NP (PRP them)) (ADVP (RB figuratively) (PP (TO to) (NP (NP (DT the) (JJ outer) (NNS darkness)) (PP (IN of) (NP (DT the) (NN unlettered))))))))))))))))))))))))) (. ?)))
Treating them poorly as if they're unlettered lets us feel better about ourselves and our superiority.
( ( ( Treating them ) ( ( poorly as ) ( if ( they ( 're unlettered ) ) ) ) ) ( ( lets ( us ( ( feel better ) ( about ( ( ourselves and ) ( our superiority ) ) ) ) ) ) . ) )
(ROOT (S (S (VP (VBG Treating) (NP (PRP them)) (ADVP (ADVP (RB poorly) (RB as)) (SBAR (IN if) (S (NP (PRP they)) (VP (VBP 're) (VP (VBN unlettered)))))))) (VP (VBZ lets) (SBAR (S (NP (PRP us)) (VP (VBP feel) (ADVP (RBR better)) (PP (IN about) (NP (NP (PRP ourselves)) (CC and) (NP (PRP$ our) (NN superiority)))))))) (. .)))