What line has to be crossed for authoritarian, or authoritative parent to be viewed as abusive?

Sometimes parents need to step in and somewhat have control over their children's life. But there can be instances when parents are going way over board and causing their kids to suffer. From a parenting action-guide website it says, "Authoritarian Parenting does not allow our children to think for themselves and actually retards and delays a child’s ability to develop critical thinking and emotional interaction skills, both of which are necessary for success in the modern world"
With that said, it is viewed to be the best idea for parents to be authoritative over their children so they can have an understanding or a word from their parents on why they are acting that way.

 http://www.preteen-thru-teenage-parenting-action-guide.com/authoritarian-parenting.html
(Parenting Action-Guide)