I think to function normally is to not be disturbed by things which bear no reasonable relation to external reality - that to me is the fundamental indication that there's something wrong, which varies from serious mental illness (e.g. psychotic delusions) to low-level depression.

It's dangerous to dismiss the whole thing as b.s., it's like throwing the baby out with the bathwater - we don't want to validate the idea that 'we can't define normal, so therefore there is no basis on which to call somebody mentally ill'.

I think a lot of the reason these things are 'soft' is that we don't have a strong enough understanding of the brain, and certainly no strong diagnostic tools to be able to analysis what's going on in someone's mind in order to determine whether something is 'wrong' for a given definition of wrong. Until then we have to hack away around the problem.

I do agree, however, that skepticism is vital in this area as in every other.