"Fever as a disease vs fever as a symptom" and "How to deal with sadness"

Historically fever was considered to be a disease itself rather than a symptom of a disease. So, when dealing with a case of fever, the doctors were trying to merely eliminate the fever rather than treating the disease causing the condition. In other words, instead of looking for a cure for what causes the main problem, their effort was focused on one of the manifestations of it.
The destructive repercussions of this assumption is predictable. The symptom would have gone while the visitor was still sick.
So it is wrong to focus on eliminating the symptom instead of the disease. Or is it? Think a bit; what bothering us is not the illness but the symptom. I am not feeling bad because some microscopic buttholes are riating and looting in my body, I am feeling bad because fever is killing me.
So it is enough to merely eliminate the symptom rather than the disease. Or is it?
As fever is a way body tries to kill those buttholes, and treating it is going to worsen the situation, it might not be the best idea. Even if fever was not helpful, if you only focus on confronting fever, there are other known/unknown symptoms left untreated.
So it is better to target the root cause. Or is it?

The very same things apply to sadness. Usually sadness is treated as a disease rather than a symptom. Sadness is not a disease, it is a symptom that something is wrong some where inside us or in the environment. And usually it is the body defense mechanism against the thing that is not right. So should we target sadness or the root cause?