by those legally entitled to act for the patient, whose reasonable will and legitimate interests must always be respected.
Note here it speaks of those legally entitled to act for the patient. As we see in some situations a child will be legally represented by a guardian appointed by the courts (I do not know how the UK terms this sort of situation).
Parents can be blinded by fear, manipulated by the unscrupulous, a thousand other things. Sometimes another party has to step in and protect the dignity, the welfare of the child.
In this case, we will never know half of the story. We know what the parents chose to make public and what appears in the court documents. We will not see the medical file nor know even a fraction of what really happened.
These things scare parents, and that is exactly the reaction the media wants. They want us to be up in arms afraid someone is going to take our child and kill it.
We need to step back and look at these things logically.
The Church never says that the parents must use extraordinary, it is legitimate for a parent or a spouse or a sibling to forego extraordinary care (do you have your durable medical power of attorney set up for someone who knows YOUR wishes?)
Still looking for the “moral right to pursue whatever extra steps they have access to” citation. What if the parents wanted to try a brain transplant from the baby in the next room. They have found a doctor who will do it. Do they still have a moral right?
Really, everyone needs to realize that this is an iceberg, we saw a small bit of it and in charity we are commanded to assume that the other parties acted in the best way they could.