What if the value of someone's life is independent of their own subjective perception of their own value? Many people, tragically, view themselves as valueless, due to many factors, but that's a reason to boost their self value, not a reason to give into their misperception of self.

If a person's body is unhealthy, we don't encourage them towards greater unhealthiness, but rather health. The same with mental health. We should encourage mentally healthy perspectives, which includes self value.