A 16-18 year old could, for example, choose not to receive a blood transfusion or to have cancer treatment, as can any consenting adult. This may well result in a preventable death. I think that's more harmful than puberty blockers.
Has the BBC made a programme which encourages children to think that blood transfusions and cancer treatment are harmful and they should refuse them if they are told they need them? Does the NHS have a special clinic where children are told that they should refuse blood transfusions and cancer treatment?
Look at what children are being told. A poster on here thought that a clip from that BBC programme was an advert for puberty blockers. I can see exactly why someone would think that, because that is exactly what an advert for puberty blockers would look like.
Children don't make decisions like this in a vacuum. None of us do, but children are particularly susceptible to believing what they are told by people who seem like helpful, responsible, knowledgeable and qualified adults.