Hi, Joshandspot. Before writing a speech, you need to have a clear idea WHO your audience is and WHAT MESSAGE you want to communicate. If you're trying to educate an audience consisting mainly of NTs, you'll probably need to include some introductory information about autism spectrum conditions and also share some personal experiences so that the audience can relate to you as a human being and empathise with your cause. Also explain what you would like them to do in order to help, and give examples and suggestions. You're right in not wanting to alienate your NT audience by blaming and shaming- it wouldn't be helpful.
I'm an English teacher (and NT- hope that's not a problem) and I've had a lot of practice in teaching people how to make speeches, so if you want any further help, just ask. Jenny