I think it boils down to some hyper-over manic feelings of their own sense of self. She somehow theartens who THEY are and there own deeds or lackthereof.
One can disagree but the vitriol directed at this amazing girl is personal to these people. Her brother made the same trip successfully when he was 16.
A study of the psychology here would be interesting. What is there in the achievement of one that so threatens the well-being of others -- non-achievers? We all have some discontent in us with our lot; unhappy with the misfortune that we are not great men and women, our endeavors are not acknowledged by the world. But many of us manifest this in a tendency to disparage the deeds of others who are more prone to greatness: bring the great men down to our level so to speak. We find this also in the envy we have of rich men -- let's tax them so that they have no more than us.
I don't really believe that the issue here is the cost to Australian taxpayers that riles some of these people. I also don't believe that the issue is whether or not the Sunderlands are perfect parents. The level of hatred -- yes, I use the word "hatred" intentionally -- exhibited on these threads about the Abby exploits must be empowered by some deeper psychological motivation. The best answer I can come up with is envy, deriving from lack of self worth.