I'm sure the airline acted in line with their policies, the policies which apply equally to every single person on that plane. You only have "a right to fly" only as long as you are able to follow the rules set down by the airline. If you cannot follow these rules then you should not be allowed to fly to protect the safety of all the other people on the flight who are willing to follow the rules.

I don't think action such as turning the plane around are undertaken lightly! It backs up flights and throws off the timing of everything leaving that airport gate for hours. I imagine this is considered an absolute emergency action.

Just because you're autistic does not give someone free pass to freak out on an airliner flying who knows how high above the earth. It's not safe and it's not fair to all the other passengers to put their safety in jeopardy for 1 person.

The kid wasn't thrown off the flight because he was autistic, he was thrown off because he couldn't follow the same rules everyone else has to.

Speaking for myself I think taking an autistic kid into an airport and onto a plane is incredibly cruel and abusive given the nature of their condition. Obviously this depends on the individual but I can't help but think it would be horrifyingly overstimulating and disturbing to them.