This doesn't make sense at all ... how can it be deemed "cruel" to try to search for alternatives, if the zero-option is to cut the life support and let the baby die? Starving the child to death sure sounds like cruelty to me.
One would believe the mission of the child protection services would be to act in the interests of the children - it seems pretty obvious that overruling the wish of the parents here certainly cannot be to "protect" the child.
The only counter-argument I can see is that they consider it better for the child to be dead than suffering. This logic commonly applies to animals, it's usually considered better to kill an animal than to leave it suffering - but humans, that's a complete different thing.
I hope there is another side of this story that I haven't heard.
They are too rigid. A lot of his problems come from seizures.
There is a treatment here (in legal states) called Charlotte's Web. Some types of epilepsy, even those where children are having hundreds of seizures a week, can be brought to a complete halt from the very first dose.
Many patients have shown a miraculous regaining cognitive abilities. One parent crying because at 10 years old she was able to "meet her son for the first time."
But heaven fucking forbid they try something like that for poor little Alfie.