Middle-class and affluent parents are good because they pass on to their children good cultural capital (such as good literacy).
Impoverished parents and working-poor parents are bad because they pass on to their children bad cultural capital (such as bad literacy).
Many, if not most people, in the U.S. embrace the above class- (and race-) based views of parenting and language (vocabulary, grammar, reading, and writing).
This ugly social mythology is identified by Pierre Bourdieu in Acts of Resistance:
I’m thinking of what has been called the “return of individualism,” a kind of self-fulfilling prophecy which tends to destroy the philosophical foundations of the welfare state and in particular the notion of collective responsibility….The return to the individual is also what makes it possible to “blame the victim,” who is entirely responsible for his or her own misfortune, and to preach the gospel of self-help, all of this being justified by the endlessly repeated need to reduce costs for companies….
In the United States, the state is splitting into two, with on the one hand a state which provides social guarantees, but only for the privileged, who are sufficiently well-off to provide themselves with insurance, with guarantees, and a repressive, policing state, for the populace. (pp. 7, 32)
But these deficit views that feed an environment of victim blaming also have been echoed in the comment section of a recent piece of mine refuting those very deficit views (see the reposting and comments at The Washington Post‘s PostEverything).
The ugliness rests on two separate and related issues—parents and language.
Parenting: Good or Bad versus Scarcity or Slack
Within a cultural of individualism, perceptions of good or bad parenting are strongly correlated with social class—as noted above. Unpacking why and how those perceptions exist reveals the ugliness.
Despite evidence to the contrary—evidence that shows class and race are more powerfully correlated with success than effort—impoverished parents are blamed as bad and affluent parents are praised as good when we assume that individual effort of those parents has determined their status.
The focus on the individual also feeds assumptions about whether or not parents can, will, or even want to provide the necessary care and initial teaching for their children. See this comment as one of several such claims:
Being poor is not the problem…..acceptance of poverty and the social position it implies is the problem. When the poor decide that they would like their children to be better off than their parents, efforts will be made in that direction…..but, if the poor decide to instill in their children the idea that being poor is better than being rich, and that the rich are the bad guys in the play, the poor will remain resentful and poor which will define them and their children.
What is often missing in all of this are the tight margins of living in scarcity (poverty) as compared to the slack of living in affluence.
For example, good but impoverished parents may appear to be “bad” when compared to poor or neglectful affluent parents who appear to be “good”—especially when we focus on proxies for the quality of parenting such as a child’s vocabulary.
Good and conscientious but impoverished parents, doing the best they can under the stress and within the tight margins of poverty, may be accurately associated with a non-standard home language, and as a result, their children may enter school with measurable literacy that is deemed behind affluent children, whose parents may have been neglectful. However, those affluent children raised in the slack of affluence may have had surrogate people and experiences that mask the weak parenting.
Impoverished parents, on the other hand, have all of their decisions and all of the factors outside of their control amplified negatively by their poverty; while affluent parents have their weaknesses masked or even mitigated by their affluence.
Class-based differences in child rearing are not “good” versus “bad,” as much as more affluent children’s rearing matches social expectations, ands thus appears “good” in that context. 
Poverty creates reduced circumstances, razor-thin margins, and relentless stress; as Sendhil Mullainathan and Eldar Shafir note, people cannot take vacations from poverty.
Affluence, however, allows slack, an abundance of time and money that buffers mistakes, carelessness, and behaviors that would otherwise be considered “bad.”
Whether parents are “good” or “bad” is profoundly impacted by status (class and race)—more so than by individual qualities alone.
The Lingering, but Flawed, Connection Between Language and Character
The related ugly is our lingering, but flawed, connection between language and character. Many in the U.S. remain convinced that vocabulary, grammar, and even pronunciation are signals of not just intelligence but the “good” or “bad” in a person.
Non-standard English is associated with race and class, revealing more about our classism and racism than about linguistics or individual character (again, read the comments section linked above).
Deficit views of language perpetuate beliefs that the poor and racial minorities speak broken or inferior forms of English; that their language is not merely different, but inferior.
Alice Walker’s The Color Purple is an epistolary novel, a story told in letters. As impoverished, black women, Celie and Nettie create a rich tapestry of using language to confront and recreate their worlds. Walker’s novel, then, is a powerful rebuking of the belief that poverty and racial minorities are the provinces of flawed or deficient language.
The impoverished do not pass on “bad,” but socially marginalized language to their children; we must admit that non-standard forms of language trigger the dual ugliness of classism and racism in the U.S.
In 1963, novelist Ralph Ellison confronted this language stereotype directly:
“Language is equipment for living,” to quote Kenneth Burke. One uses the language which helps to preserve one’s life, which helps to make one feel at peace in the world, and which screens out the greatest amount of chaos. All human beings do this.
Further, Ellison rejects the deficit view held about the language of poor blacks:
Some of us look at the Negro community in the South and say that these kids have no capacity to manipulate language. Well, these are not the Negroes I know. Because I know that the wordplay of Negro kids in the South would make the experimental poets, the modern poets, green with envy. I don’t mean that these kids possess broad dictionary knowledge, but within the bounds of their familiar environment and within the bounds of their rich oral culture, they possess a great virtuosity with the music and poetry of words. The question is how can you get this skill into the mainstream of the language, because it is without doubt there. And much of it finds its way into the broader language. Now I know this just as William Faulkner knew it. This does not require a lot of testing; all you have to do is to walk into a Negro church.
Also unmasking deficit views of language related to class and race, in 1979, James Baldwin asked, “If Black English Isn’t a Language, Then Tell Me, What Is?”:
The argument concerning the use, or the status, or the reality, of black English is rooted in American history and has absolutely nothing to do with the question the argument supposes itself to be posing. The argument has nothing to do with language itself but with the role of language. Language, incontestably, reveals the speaker. Language, also, far more dubiously, is meant to define the other–and, in this case, the other is refusing to be defined by a language that has never been able to recognize him.
Like Ellison, Baldwin recognizes poetry where others see deficit:
Now, I do not know what white Americans would sound like if there had never been any black people in the United States, but they would not sound the way they sound. Jazz, for example, is a very specific sexual term, as in jazz me, baby, but white people purified it into the Jazz Age. Sock it to me, which means, roughly, the same thing, has been adopted by Nathaniel Hawthorne’s descendants with no qualms or hesitations at all, along with let it all hang out and right on! Beat to his socks which was once the black’s most total and despairing image of poverty, was transformed into a thing called the Beat Generation, which phenomenon was, largely, composed of uptight, middle-class white people, imitating poverty, trying to get down, to get with it, doing their thing, doing their despairing best to be funky, which we, the blacks, never dreamed of doing–we were funky, baby, like funk was going out of style.
Ultimately, then, Baldwin states boldly his own recognition of the ugly:
The brutal truth is that the bulk of white people in American never had any interest in educating black people, except as this could serve white purposes. It is not the black child’s language that is in question, it is not his language that is despised: It is his experience. A child cannot be taught by anyone who despises him, and a child cannot afford to be fooled. A child cannot be taught by anyone whose demand, essentially, is that the child repudiate his experience, and all that gives him sustenance, and enter a limbo in which he will no longer be black, and in which he knows that he can never become white. Black people have lost too many black children that way.
And now we are still confronted with “the brutal truth,” as Baldwin puts it. Why do we cling to deficit views of poverty and language, and why are so many angry and bitter toward people—families and children—who find themselves in poverty—while simultaneously praising the affluent?
It may well be that neither the quantity or quality of words children bring to school nor that both are strongly correlated with the socioeconomic status of those children’s parents matters as much as our cultural bitterness, callousness.
More important is how adults use words to demonize the marginalized and create an Other so that they do not have to confront themselves.  Again, if you doubt me, return to those comments that suggest to me that if we wish to judge parents by their children, there we have ample evidence to draw some pretty harsh conclusions.
 See Annette Lareau, Unequal Childhoods: Class, Race, and Family Life, who explains about the differences in child rearing by class between middle-class and working-class/poor families:
The differences are striking….
Neither the approach of concerted cultivation or the accomplishment of natural growth is without flaws. Both have strengths and weaknesses [emphasis added]. Middle-class children, for example, are often exhausted, have vicious fights with siblings, and do not have as much contact with their extended families as working-class and poor children. But when children enter institutions such as schools and health care settings, the strategy of middle-class child rearing of concerted cultivation is far more in compliance with the current standards of professionals than is the approach of the accomplishment of natural growth. There are signs that middle-class children gain advantages, including potentially in the world of work, from the experience of concerted cultivation. Working-class and poor children do not gain this benefit.