1. On racial matters, Finch is a moderate, neither aware of the history of race relations in the south nor interested in more radical change.
2. The centerpiece trial of Tom Robinson relies on replacing the bias against black people with the bias against poor whites.
3. The treatment of Boo Radley is an unconscionable lie.
The answer to all three concerns, I believe, is "unreliable narrator."
A typical piece of evidence for the first charge is as follows:
He likes Walter Cunningham. Cunningham is, to his mind, the right sort of poor white farmer: a man who refuses a W.P.A. handout and who scrupulously repays Finch for legal work with a load of stove wood, a sack of hickory nuts, and a crate of smilax and holly. Against this, Finch must weigh the fact that Cunningham also leads lynch mobs against black people. So what does he do? Once again, he puts personal ties first. Cunningham, Finch tells his daughter, is “basically a good man,” who “just has his blind spots along with the rest of us.” Blind spots? As the legal scholar Monroe Freedman has written, “It just happens that Cunningham’s blind spot (along with the rest of us?) is a homicidal hatred of black people.”
Gladwell is mis-handling the relevant question, which is: how does one best explain racial injustice to a child? The methods one might use with adults--appeals to a notion of justice, etc--aren't appropriate, because Scout's not developed enough to appreciate all the dynamics involved. However, it is also worthwhile to pass along the lesson that all people are people, which means they have both flaws and redeeming qualities. Atticus is right to be teaching that lesson, especially since it's one Scout has been having trouble with (she picks on a kid in school for being different earlier in the book, as I recall). It will serve her better to learn that lesson first. If one thinks of the Jim Crow racist as irremediable, then the work of justice is only going to be a work of force: one can neither reason nor appeal. But the point is surely that both approaches are needed--a constant request for what justice demands and the slower work of transforming society person by person.
On the trial, there's a point worth bringing back from the above paragraph: we're looking at the trial through Scout's eyes, and Scout, as Gladwell points out, though he doesn't quite realize it, regards the Ewells as trash (“Every town the size of Maycomb had families like the Ewells,” Scout tells us. “No truant officers could keep their numerous offspring in school; no public health officer could free them from congenital defects, various worms, and the diseases indigenous to filthy surroundings.”).
The rest of the analysis rests on believing Tom really did rape Mayella, in which case Atticus' appeal to class bias makes sense. But if Tom didn't do it, the absence of exculpatory evidence doesn't mean quite so much--here Gladwell confuses the fact that the presentation of Tom's injury is for the reader the decisive fact--we never know anything about what the jury thinks. It also may be the case that the mention of Mayella's relationship with her father was real, and Tom's real offense was pitying a white family in public. There's no particular reason Gladwell offers to find one reading more compelling than the other, based only on the text.
On Boo Radley, Gladwell's analysis has to overlook the fact that Ewell's solution to Atticus' humiliation of him is to try and kill his children. It's into this breach that Atticus and the Sheriff have to step. Alternative hypothesis time: perhaps they both feel genuinely bad for the Ewell family as a whole, and perceive that suicide is a less-embarrassing explanation to give that what actually happened. Again, there's no reason, on the text, to prefer one reading to another.
Again, the unreliable narrator emerges. If the book were written in the third person, I'd find some of this criticism more compelling, because there would be a stable body of facts to which one side or the other could appeal. But coming as it does in a first-person, one cannot really talk about the story without talking about Scout's perception of it. Moreover, a novel gets a partial claim to suspension of disbelief: sometimes we have to take the author's word for it.
In a sense, this is a missed opportunity for Gladwell. His underlying point about the problems of moderate, meliorist solutions to deep issues of justice is well-taken (see also the discussion of the weaknesses of Walzer's theory of critics here). It's true to say that Atticus, as far as we know, represents no radical threat to the system in which he finds himself. An article which took him at his word and nevertheless attacked the perspective he represents would have been quite interesting.