That's an excellent question. It's one of the points we tried to clarify in our paper.
There are indeed some extremely invasive types of treatments in psychiatry. One example is implanting a vagus nerve stimulator. This is a device implanted in the brain. Some people might decide that it's too invasive for them. That should be clarified.
We have access to a fairly broad set of psychiatric treatments in Canada. I would say that in general, people hesitate because of a misunderstanding or misinformation. Take the example of electroshock, also known as sismotherapy. This treatment is extremely effective for major depression and is used regularly, but it carries significant social stigma. Often, people who are misinformed will refuse it. Personally, I offer this treatment to certain patients. When you take the time to sit down with them and adequately explain its usefulness, they usually understand it well.
Sometimes, an individual refuses treatments like those because they deem them unacceptable. Generally, however, it is possible to walk them through it, thoroughly illustrate the benefits these treatments can provide, and explain how tolerable they are compared to all the treatments available in physical medicine, which are often very invasive as well.