> Arguably "worrying too much" is a symptom of depression, rather than a cause.

Well, it's not like you're suddenly getting a depression out of the blue and then start having obsessive negative thoughts. Repetitive intrusive thoughts can in fact lead into depression.

> Are you just saying that worrying about the state of the world makes you fed-up?

Most people will probably just feel fed up and not bother much. But for some, it can contribute to anxiety, depressive episodes or a full depression.

I agree, the term "depression" is probably used inflationary when it's "only" a depressive episode or feeling depressed.