They are not. They are living their lives in the only ways they know, and the challenge is to meet them at their points of need if/when they might actually wish to try to achieve some varied or different results.

The autism diagnosis first entered the picture only in relation to low-functioning people who were truly disabled far beyond the display of merely-odd or -quirky behaviours...and I would view something such as a high-functioning person re-arranging food on a plate prior to eating -- I sometimes do that -- as no big deal as long as the meal is ultimately eaten in a relatively timely manner. So the challenge for you, in at least my own opinion, is to carefully distinguish between what *you* might want (either for yourself or for someone else) wherever no harm is actually being done...and there are times when telling someone he or she is autistic can actually be harmful.

note: No accusation is being made here, just a reminder of "...different, not less [or defective]" from the story of Temple Grandin.