Perry is learning to communicate effectively with the world around him - a tough task for a child with autism - and he is with his mother.
This is going to sound cruel, but honestly, I have no "soft" way of saying this... it isn't my responsibility to make sure that every child learns basic communications. Now, yes, this child has special difficulties. But I'm walking down the street, I may not even know that. All I know is that a child I don't know is addressing me. I ignore it for safety reasons, because I avoid interaction with children I don't know, because these days anyone childless who interacts with children they don't know are seen by many to b at least a little creepy.
I am definitely on the side of it being rude to ignore someone who has greeted you, except when you're doing so for personal safety.
And yet the point has been made... repeatedly... that one needn't be obligated to enter into an interaction. When the telephone rings, that is a greeting. It's a "handshake", between your phone and theirs. It's the telephonic equivalent of a friendly wave. But just today, the point was made on these forums that "just because the phone rings doesn't mean you have to answer it."
Likewise, a knock on your front door is a form of greeting. And yet again, the point has been made that just because someone knocks at your front door doesn't mean you have to answer it. Even if they can see you clearly through a plate glass window that faces the front of the house and the curtains are wide open for all to see, it's been stated that it's not rude to ignore that greeting.
However, now we're being told that just because we are greeted on the street by people we don't know, we are required to respond in kind, or we are rude (no ifs ands or buts). Why is it true for passing strangers, but not the telephone or the front door? Is it because they see you out and about? That seems rather arbitrary. We're told we should even be interrupting our own phone conversations (incredibly rude, to my mind) to return an unsolicited greeting from someone whom we don't know. That doesn't seem very polite to me.
Just because I'm not in my house, doesn't mean that I'm not allowed to set personal boundaries. You have every right to greet me, but that right ends at my airspace... you have no right to expect a greeting in return. If a greeting *is* returned, that is a pleasant courtesy. But it is not a requirement.