What's wrong with teaching an autistic son the right values?

I got into a minor verbal skirmish with a young mother with an autistic kid. From Wikipedia, Autism is a brain development disorder characterized by impairments in social interaction and communication, and restricted and repetitive behavior, all exhibited before a child is three years old. These characteristics distinguish autism from milder autism spectrum disorders (ASD). To put it simply, someone who is autistic has difficulty communicating and interacting in a social environment. We were on the topic of wasting food. She started off by commenting how she felt guilty because she often wasted food through overcooking. Personally, I am against wasting food. We are all familiar with those stories of poor starving children (and adults) and I am thankful, very thankful, that I have no need to go hungry (yet). As such, I commented that it was "good" that she felt guilty. This means there is still hope. And so, I suggested that she cuts down on the amount of food she cooks. Alternatively, she can force herself to overeat just so that she would finish all the extra food. This way, she can take it as a lesson and remind herself not to waste food the next day. Despite my clarification that I was not trying to put her down - but just looking at the subject matter of wasting food - her reply didn't sound too happy. She then explained that she has an autistic son. Because the amount he eats is always a question mark, she chooses to overcook to ensure he will not go hungry. Fair enough. I didn't know that so I concede the point. I offered another suggestion that there is really no harm trying to "make her son feel guilty". After all, it would be a good thing if she manages to get through to her son and help him grow up to be a considerate member of society. Her subsequent reply became more livid. It conveyed the idea of "HEY! I GOT A DISABLED SON HERE SO I RATHER DIE THAN MAKE HIM FEEL GUILTY." I have to be honest here that I do not have much experience with autistic children. In case anyone misunderstands, I have no prejudice towards them. If I have to give an opinion, I am honestly very thankful that I was born more privileged. In the exchange with this mother, what I cannot understand is why we can't try to make the child feel guilty for wasting food. I don't mean literally playing the devil and poking him with toothpicks till he understands. Rather, what harm can there be in imparting the right values to the child? What has autism got to do with anything? Does having an autistic child gives you the right to scorn the world? Does having an autistic child gives you the right to insist you are right? Does having an autistic child means <fill in the blank>? But I guess it may be the mother instinct in her that was speaking. To move forward in front of her son to protect him. God bless.