As an early childhood educator, I've become wary of blaming everything on a child's upbringing.
Over the years, I've worked with numerous children with ADD, ADHD, behavior disorders on the autism spectrum, sensory integration issues, etc.
These things are not uncommon today, if they ever were. I have children with diagnosed behavioral special needs in my class every single year; often more than one. I'd say at least one out of ten children these days has some sort of behavioral issue.
Part of it is that high-functioning autism spectrum disorders actually have become more common. No one knows why. Some people suspect immunizations cause autism (I don't buy that theory). I think it's a combination of things: more parents having children at an older age. More preemies surviving through medical technology. Maybe doctors are also just getting better at diagnosing high-functioning autism, whereas in the past a child with this type of disorder would simply have been labeled "bad", "disobedient", "antisocial", "weird".
Of course, there are things parents can do to mitigate some of the behavior that goes along with these problems, things a parent can do to improve the child's chances of succeeding in school and in life. Most of these children will grow up to lead "normal" lives, with jobs and families of their own.
But to blame the parent entirely for any of the manifestations of these disorders is not fair to the parent.
These parents have a tough enough row to hoe, without that. I'm sure people look at their children acting out in public and make comments and judgments about how the parents just aren't doing their job, when in fact the parents are working ten times harder than parents of children without behavioral issues.
Of course, on the other hand, there are disobedient, disruptive children who have no diagnosable disorder. Their behavior may well be the result of a lack of discipline on the part of the parents. But it's hard to tell; behavior disorders often appear, to outsiders, like simple "bad behavior".
To complicate matters, children with behavior disorders often are not diagnosed or treated until they start elementary school at age 5 or 6, or even older. Although children who are diagnosed earlier tend to do better.
Anyway, that's my 2 cents: not always the parents' fault, and almost impossible to tell (without knowing the child and the family) whether it is or isn't.