We are more than "fairly" close on this. I agree with all of your points on this. I agree that it is so rare that a child expresses permanent hate and rejection of a loving parent WITHOUT alienation, that it is fair to presume that alienation exists in such situations until proven otherwise. I also like your next point:
"Another way it could be viewed by the courts is as 'all part of growing up' to hate one or other of your parents at some stage in your early life. Then hopefully the parent-child relationship could be saved or salvaged with a bit of coaxing."
What child choice does is that it forces permanent estrangement out of typical, unavoidable teenage angst. There will always be an occasion where a teen slams their bedroom door screaming "I hate you!" (usually because the parent is doing something a parent is SUPPOSED to do). But the animosity is forgotten within hours or at least within days. Family court, in support of permanent hate over loving relationships, will lock the family into inescapable dysfunction.
Why does the court do this? Because they are misguided; because they are listening to lawyers, not their hearts and their own experience and because the law TELLS them to consider the preference of the child. Family law also dictates that when a parent and child are in conflict, that the parent is wrong, but that is rarely the case. Parenting is not a popularity contest and sometimes tough love is more important than trying to be the "chosen" parent of preference.
I could write an encyclopedia about what is wrong with the "preference of the child" statute, so you will have to stop me.
Unfortunately you fall back to the dead CBI argument: "Can any proposals for family law only be based on this idea - that the system must lead to whatever our society or our leader believe is going to be the best for children? You would say yes straight away"
No, because you still insert superlatives: The combination of "only" and "must" are like saying that NOTHING else can ever be a factor in any court consideration. That would be preposterous. Besides, who said I have so much confidence in what "our leader" believes?
Here is ultimately where you always fail: "To return to my comment about all proposals for family law having to produce an outcome that is ultimately best for children (albeit that I believe moving away from the BIC test is the only way to achieve this in many cases)."
This is a hypocritical statement. You are saying that you want to get away from doing what is in children's interests for the sake of children's interests. Why are you fighting children's interests again? You just showed that you DO consider the interests of a child important. You can't say that you support something and oppose it in the same statement.
Excuse the double negative, but the "example" you gave is NOT an example of why we should not consider the best interests of a child. As you specifically acknowledged, it is an example of the opposite: That we should condemn child choice because we promote the interests of children.