I don't see why laughter would be warranted for such a question. Yeah, MRIs are expensive, but wouldn't measurement of the brain's internals among those with autism be helpful in identifying the contributing factors and - maybe someday - a proper treatment?
Parent post is talking about scanning an individual. That's less useful. The second link I provide gives some reasoning: ASD is often suspected early. Many parents recognise somethings are different at about two years of age. You can't put an awake two year old in an MRI machine because you need the scanned person to stay still.
