The parents are blameless as regards the surgery, yes.
We know that there is a growing consensus on the social contagion of ROGD. Kids (especially but not exclusively girls) who would have been "emo" in years past, or anorexics, or punks, or hippies etc. are now becoming "trans" instead.
For many, this goes as far as a haircut and a coming out as "enby". But for some, usually those with something else going on, like a mental health issue or a neurodevelopmental disorder, it goes further.
Parents who could previously let their little emo kids drown in kohl pencil and weird haircuts are now facing huge pressure from society, schools and their own, indoctrinated, script-holding children, to pay great "affirmative" attention to their child's teenage phase.
They don't know where to turn when faced with threats of ending up with a "dead daughter" if they don't go along with their "alive son" (or vice versa), so they turn to health professionals—people who are ostensibly there to look out for the best interests of their patients—for help. Often they are immediately, and with very little exploration of alternative explanations for their child's distress, set on a course of affirmative care that will see their children medicalised and surgically altered. And they go along with it, partly because they are bombarded on all fronts with threats that their children will die if they do not, and partly because they trust health care professionals and don't realise that what they are doing is akin to starting chemotherapy on the basis of a bruise.
I understand your point about taking a broader view in terms of the causes of the ongoing transing trend among youngsters. I personally feel that little girls and little boys are receiving dreadful cues from society that are made all the worse if they're GNC. It must be devastating for the bookish little girl who likes rolling in mud and doing woodwork to look around at her Love Island worshipping piers and feel like she is "wrong", just as it must be awful for a tender, sweet little boy to look around him and see a society that brands him as "toxic" before he's even learned to read. I count myself supremely lucky that when I was a GNC little girl with undiagnosed ADHD in the 80s, my mother cut my hair, let me roll in mud, and bought me magazines about bugs instead of trying to "fix" me or telling me there was something wrong with me.
But all of that withstanding, I cannot and will not blame parents for trusting medical professionals. We should be able to do that. We should at least be able to do that. So for as long as the medical professionals to whom these parents go, desperate and confused, continue to push children along an experimental path they know to be a one-way street to lifelong medical dependence (and they must know), the majority of the blame lies with them.
Perhaps they're not individually legally liable, but someone, at some point, must be. Because anyone with an ounce of sense could see the harm coming from a hundred Reddit posts away.