Forget about calling it mental healthcare or not: Most people end up dealing with people in significant distress at one point or another. Many do it all the time even when they aren't trained or getting paid as mental health professionals, just because of circumstances. You don't need a clinical setting for someone to tell you that they have suicidal ideation, or to be stuck interacting with someone in a crisis situation. We don't train every adult in this, but the more you have to do it, the more you have to learn some tools for at least doing little harm.

We can see an LLM as someone that talks with more people, for more time, than anyone on earth talks in their lifetime. So they are due to be in constant contact with people in mental distress. At that point, you might as well consider the importance of giving them the skills of a mental health professonal, because they are going to be facing more of this than a priest in a confessional. And this is true whether someone says "Gemini, pretend that you are a psychologist" or not. You or I don't need a prompt to know we need to notice when someone is in a severe psychotic episode: Some level of mental health awareness is built in, if just to protect ourselves. So an LLM needs quite a bit of this by default to avoid being really harmful. And once you give it that, you might as well evaluate it against professionals: Not because it must be as good, but because it'd be really nice if it was, even when it's not trying to act as one.