This website was made so people can learn a lesson from my life. Parents should definitely tell their child(ren) about their diagnosis. It's very important so they can know why things are the way they are. Defense mode is a very important thing to understand both for the parent and the child. Also, don't look at the DSM. Instead, look at www.aspergersexperts.com. They have everything there including resourses, explanations, forums, coaching, therapy, etc.
I recommend professionals look at this defense mode course to understand that people can look like they're doing things just to be mean but really, they're in defense mode and just scared.