I am trying not to judge you because raising a kid on the spectrum is hard for parents, but my special interest is an incredibly meaningful part of my life. It has drawn me out of myself, given me confidence, helped me make like-minded friends, and made me a member of communities. It is also how I make money. A lot of aspies have stories like that. You should consider them before you try to drug away a huge part of your child's identity. If his special interest is making it impossible for him to function, you have to choose what you believe to be the lesser of two evils. If you just want him to be more normal, trying to do this to him is just evil.