Capacity isn't a global issue and doesn't apply to every circumstance. Different medications, therapies, ECT, psychosurgery etc all have different rules.
It is not assumed that being under section means you don't have the capacity to make any decisions or that you have no rights. The mental health act and mental capacity act are complex legislation.
Sec 2 for example is a section for assessment so you can't administer medication without consent unless in an 'emergency'. A Sec 3 is for treatment but even then, if the patient is still not consenting to medication after 3 months, the psychiatrist has to state their intention to continue to enforce medication without consent and a second opinion is required from another psychiatrist who reviews the notes and meets with the patient and agrees or not.
You can't be forced to have medical (physical) health treatment under any section for example unless under specific legislation of the MHA where it is proven that the refusal for the medical treatment is directly related to the mental disorder that you are being treated for. NG feeding for anorexia nervosa patients starving themselves to death is the most common example where medical treatment is enforced without consent under that legislation.
So in the case of the person I mentioned earlier, they were being treated for a personality disorder. They were able to refuse treatment for cancer because their capacity to make that decision was assessed, they demonstrated full understanding of the proposed treatment and the potential consequences of not having it and their refusal to accept cancer treatment was not consdered to be related to the mental disorder they were being treated for.
A person can be required to remain on the unit under section but the fact is that if they did leave and returned home and refused to return to the hospital, they could be discharged. Because using the Police to force entry into someone's home to return them to hospital requires a warrant issued by a magistrates court where it has to be proven that not doing so would result in serious harm as the person would be unable to look after themselves. I can't count the number of times when I was working in inpatient, that someone under section went AWOL and we discharged them after 48 hrs and used their bed.
I am not proposing 'euthanising' anyone nor suggesting anyone be 'chosen to die'.
I'm talking about the individuals who would be able to say "I relive my CSA in flashbacks every single day, I've been in hospital for X years, I've tried X number of treatments, nothing has helped. I feel tortured and I want to die".
Because currently we say 'tough shit' to those people and force them to live miserable lives on specialist units, watch them bath and use the toilet, give them a TV in a perspex box to watch and give them plastic plates and plastic cutlery to eat with. Remove anything that they could use to harm themselves and then when they're banging their head on the wall trying to stop the horrible images in their head (we can't remove walls!) we have a bunch of staff pin them down on the floor which really reminds them of their CSA btw and wait till they've tired themselves out or pull their pants down a bit which again reminds them of CSA, to give an injection into their buttock and hopefully make them too sedated to try to harm themselves.
Then do it again the next day or a few days later. For years. That's why I felt abusive.