If I wasn't on guard, prepared to devote thought to the question, I'd have accepted any of those answers - but this article makes it easy to see how those different goals can be in conflict.
If I had to come up with the best answer I could, I think I'd settle on "A psychologist's mission should be to prevent a person from actively harming the physical health of themselves or others, even taking into account reasonable expectations of future harm based on current activities. And additionally to help make any adjustments that the patient requests." So, sometimes it's okay to involuntarily treat, but only if there's a present or soon-to-be present physical danger. Otherwise, only help them with the things they want fixed.
(Note: I once had a long and coherent conversation with a guy who knew he was the messiah promised to the jews, descendant of david, future king of the world. It was an unavoidable fact. Him being a young, black presbyterian had no bearing on the issue. He had lots of evidence, much of it delusional, and much of his reasoning was based on bad information that he was literally incapable of doubting. But in the end, his delusion was immensely satisfying to him, and his life was otherwise boring, banal, and from an outside perspective, depressing as hell. And from what I can tell, as long as he doesn't travel to Israel and get a jewish girlfriend, the more dangerously bizarre parts of his prophecies won't begin, so I just decided to wish him well and let it go.)