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))))))))))))))))))))))))) (. ?)))
They can read and write, but they aren't exactly polished, so we treat them as poorly as those who can't read and write.
( ( ( ( ( They ( can ( ( read and ) write ) ) ) , ) but ) ( ( ( ( they ( ( are n't ) ( exactly polished ) ) ) , ) so ) ( we ( ( ( treat them ) ( as poorly ) ) ( as ( those ( who ( ( ca n't ) ( ( read and ) write ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (PRP They)) (VP (MD can) (VP (VB read) (CC and) (VB write)))) (, ,) (CC but) (S (S (NP (PRP they)) (VP (VBP are) (RB n't) (ADJP (RB exactly) (VBN polished)))) (, ,) (IN so) (S (NP (PRP we)) (VP (VBP treat) (NP (PRP them)) (ADVP (RB as) (RB poorly)) (PP (IN as) (NP (NP (DT those)) (SBAR (WHNP (WP who)) (S (VP (MD ca) (RB n't) (VP (VB read) (CC and) (VB write)))))))))) (. .)))