Downs syndrome is an objectively identifiable genetic abnormality, as I understand it.
There is no objective medical test to diagnose depression. “Clinical Depression” is medicalized misery. We should offer people copious amounts of help; it should not be forced upon them.
According to psychiatrist Thomas Szasz, psychiatric coercion is medicalized terrorism.
I recommend you read or at least read a summary (like in the Amazon description or sample) of the book Anatomy of an Epidemic by Robert Whitaker.