They're detailing how it's highly unpleasant, and in some ways arguably draconian, to be "sectioned", because (again, "in some ways") the individuals suffering it have less autonomy and receive more "punitive detention" style of treatment than actual criminal prisoners do.

Because, contrary to an idealistic public view that mental health is taken care of when discovered, the reality is that it's a system that has little recourse or solution other than to medicate into dullness, and if acting-out requires it, into virtual sedation and lockdown. With all personal rights and dignity gone by default.

Most people who went through it would come out traumatised if they weren't already to start with. It's not treatment the average person would give their dog.