"Given a choice between my daughter reading Harry Potter and watching MTV, I'll take Harry Potter."
That's good because you have control over what she is exposed too and I'm sure have pointed out that it is fiction, and not truth.
But, like I said, many parents are not involved in the rearing of their children and the children are left to be raised by society. Mostly in the form of peer pressure and review.
That's where the danger lies.
In that case, the content of books like Harry Potter are the least of their worries. Parents who fail to actually do parenting are dooming their children to be rudderless, amoral, and unable to exercise self-restraint.