How much influence do parents have in developing their children's attitudes and beliefs, especially in the first 20 years, and at what point do we begin to hold the child responsible for those traits as an adult?

For better or worse.

If the child is raised to be an awful person, because that’s what his parents expected of him (whether they know it is awful or not) at what point do we start blaming the “child,” the offspring for their own behavior, which was taught?

I understand some kids just turn out the way they turn out, really through no fault of the parents. But let’s set that aside, and focus on the parent deliberately raising a child a certain way,for example, to be racist or intolerant or sexist, etc.