"The social worker didn't coerce anybody."
Just to make sure I understand, what you are saying is that if you were in this same situation you would desire to have someone else make this decision for you and your family. For example, if you believed that radiation treatments were the best choice you would rather have a judge decide if that's best or if maybe there was some other therapy he could choose that. You might decide a certain course of action is best but you believe that it would be better to have a judge make the final decision for you.
After all, that is what you are prescribing for this family, so I assume that you would want this for yours as well in a similar situation.
I haven't faced this type of situation, but the point is not what the parents want, the point is a reasonable degree of state protection for the child. In this case, it was reasonable for the state to scrutinize the situation, and also reasonable to conclude what it did -- that in this case, the child was competent to participate in the decision-making, and that the parents and child were willing to undertake an alternate type of treatment which, while not the first choice of mainstream medicine, would be under the direction of a legitimate medical professional and completely unreasonable, and that the state should NOT coerce the family into pursuing the recommended therapy they had already tried once and did not want to try again. The state did not yank the boy out of his home while the proceedings were underway.
However, there are plenty of cases -- often discovered too late for the child -- where parents are undertaking dangerous "therapies" for their children, and/or withholding therapies that provide an excellent or even virtually certain chance of saving the child from dying before reaching adulthood. The 4 year old girl who died from "forced water drinking therapy" and a 10 year old girl a few years earlier who died from "rebirthing therapy" (smothered to death while rolled up inside a heavy blanket from which the idiot "therapist" and mother were forcing her to struggle to get out of in a supposed re-enactment of birth), are two examples. Another family starved an infant to the brink of death, and to certain brain damage, by restricting it to a bizarre vegan diet that the parents believed was healthy. I would certainly find it appropriate for the state to respond to those tragedies by tracking down any other families who were participating in "therapies" under the direction of the same "therapists", or imposing such clearly non-life-sustaining dietary programs, and ensuring -- coercively, if necessary -- that they cease doing so.
Would I want the state to intervene if I was one of the idiot parents doing this crap to my kids? Of course not. But being sane, I most certainly do want the state to investigate reasonable suspicions of serious child abuse/neglect, and intervene if investigation finds clear proof that intervention is necessary to protect the child from severe harm. Are there going to be gray areas, where the state may step over the line, inappropriately imposing its own values or pursuing investigations which turn out to be unfounded? Yes, but that's not a reason to abandon the whole concept of state intervention in situations where there is reasonable suspicion of child abuse or neglect. And it is a reason for reasonable parents -- like the ones in this case -- to cooperate with reasonable legal proceedings.