Well, I wouldn't call it greed exactly. It is natural for a parent to want to keep their child happy. That is especially true if that child has some form of emotional problem. This is the sad part, autism or no autism, society and life places limits on things. Yes, a child may have a melt down if they cannot get what they want, but, that doesn't mean that it is always going to be available to them. Somewhere, sometime, someone is going to say no and stick to it. Like you can train an animal that really doesn't have a reason factor, they don't understand or grasp the meaning of time, it doesn't matter, they are trained to accept what life gives them. I don't see how always catering to the unreasonable desires just because they don't have a concept of fair or unfair, is a very nice thing to do to that person. They continue to grow up and at some point their advocacy group will no longer be there to scream until they get their own way. Eventually the person learns what no means and meltdowns are not going to change anything.
I don't think that Disney or any other location should be forced to make one persons desires override the needs and desires of everyone else no matter how loud they might yell. It just is a bad way to set that person up for a very bad experience later on. It appears to me that most places and Disney in particular have taken steps to accommodate beyond the letter and even the spirit of the law. Those that try and push it beyond that have probable good intentions, but, for the sake of fairness and common sense, sometimes the answer should be a loud resounding NO!