This is all about 'dignity'.
What sort of dignity? Right-to-die campaigners condemn the lives of the disabled as bereft of dignity, apparently associating dignity solely with control over bodily functions. According to this definition, if someone loses their bodily 'autonomy', they no longer have human dignity. In my mind, dignity comes from bearing up under suffering we meet throughout our lives rather than letting it destroy us, and from facing fears rather than caving in to them.