I believe that students on the autistic spectrum, whom are passionate about a particular topic, are this way because it feels safe and they understand the hidden rules of that passion. Please note, just because a person has autism doesn't mean they have a particular passion. If you know one person with autism, all that means is that you know one person with autism. As educators, we need to tap into these passions and encourage students to explore within them. If you are doing a unit study on writing non-fiction, have the student write a non-fiction piece about their passion. If you are studying a particular genre, help the student find books within that genre pertaining to the passion. These suggestions may not work every time, or with every students. However, I think they are a place to start, in terms of thinking about creative ideas to empower students within their passions.
I think a great analogy for only wanting to read or write about the same passion is a roundabout. Some drivers instantly know what to do without any directions, they are not scared of the unknown and willingly embrace it. Some drivers panic because the traffic won't slow down and they end up going around the circle multiple times, but with some quick observations they figure it out. Then there are people like Chevy Chase in National Lampoons European vacation, no matter how hard they might try to get off the roundabout, it's almost easier just to stay on and observe the sites (Look kids! Big Ben, Parliament!). Students with intense passions are those people like Chevy Chase (see clip below). As educators we need to support them, within their passions, and remember never to force them outside of their passion. Imagine if Chevy Chase's wife would have taken the wheel and forced him to turn left. That would have been dangerous for everyone involved.
As a whole, I think educator do a great job of autism awareness. However, we need to move from just being aware to being accepting. These students aren't purposely trying to break rules (whether it be a school rule or expectations around an academic assignment). If anything, they are trying to navigate their life in a way that fits the hidden social rules of everyone around them. One way we can empower them, within their learning, is to differentiate assignments within their passions. I encourage you to give it a try. Does it make a difference to that student? If so, than I believe it is worth it!
A great resource, for more ideas on positive ways to support student's passion is Just Give Him the Whale by Paula Kluth.