I agree it’s all coercion.
That’s largely what the Mental Health Act is for. To force people to have treatment. Some people would say it’s unethical for that very reason. But their view has yet to become the orthodoxy. Some people might equally argue it is illogical to have a law to force people to have mental health treatment, but not physical treatment. But our society, and our law, have (rightly or wrongly) long tended to see the two as different.
The Mental Capacity Act isn’t meant to be about coercion - although in certain circumstances it permits things which are coercive provided they are in a person’s best interests.
You can’t use coercion to obtain consent - because compliance obtained by coercion isn’t true consent.
But where consent isn’t an issue - either because the MHA dispenses with the need for it, or because a person lacks the relevant capacity - some form of coercion may well be legally and ethically justifiable and appropriate.
But that doesn’t make all forms of coercion equally acceptable. Some are basically always unacceptable - in this country, at least, you’d never succeed in justifying waterboarding a patient to make them take their medicine, or threatening to kill their dog, for example. But inevitably there will always be a large grey area where choices have to be made, governed by legal principles (eg least restriction in the MCA), ethical conventions (eg what the professional consensus deems acceptable) and personal ethical intuitions.
Apologies if I am missing your point completely.