I think some of these posts might be inadvertently debating dualism, "the philosophical position that mental phenomena are non-physical." You're arguing whether depression is caused by emotions and thoughts vs biology (mind vs brain), when Neuroscience doesn't make a distinction. Emotions and thoughts are biology - serotonin and glutamate and neurons are not considered to be separate from behavior, they are how behavior is encoded. In Neuroscience, the mind is usually considered an emergent property of the brain.

It's like arguing that a bug is a problem with the UI, not the code...

https://en.wikipedia.org/wiki/Dualism_(philosophy_of_mind)