Parenting as we know it is a horrid thing.
Children are dehumanised - parent knows best. You may say the parent usually does, and that's true, but usually the child doesn't disagree with his parent. In cases of a conflict, when a child is sufficiently confident to contradict his parent, his view must be taken seriously, just like one would listen if a friend thought you were in error.
Many parents consider children like clay to be sculpted into a good adult (read: valid person). This also dehumanises children who are people now. A child has preferences of his own, and these must be taken seriously, not the preferences of some imagined future person.
Parents believe that people can't always have what they want. In practice this is a transparent excuse to deny things to one's child. In principle, it says people are doomed to unhappiness. This is not true. Through a combination of creatively solving problems so people are better able realise their intentions and wants, and creatively analysing and changing their intentions and wants to better, more realisable ones, people can be very successful. There is nothing stopping them; the limiting factor is just their skill (morality).
Parents so often treat their own desires as unquestionable, unalterable truth, and from this point of view declare their children's desires impossible. Examples include the mundane (but still important) like a parent who insists he can't stand even the sound of violence and bans many movies from his home, or a parent who hates messes and insists child meticulously clean his room (why the child should clean the mess the parent hates is unclear). Another example would be a parent who says "I will feel like a failure if you do not graduate college, so you must go." Isn't it obvious this is the parent's problem and the solution is almost certainly for the parent to get over it? (unless child doesn't mind college, in which case parent is lucky and need not address his flaw) Sadly it is not.