Also depression is in and of itself dangerous. Even avoiding the entire topic of suicide, depression can lead to a variety of self destructive behaviors and poor decisions. Additionally plenty of people suffering from depression will naturally 'self medicate' with drugs that don't actually address the underlying neurological issues that ketamine might, and certainly can cause physical harm.
I think it's somewhat odd that in the 21st century we still aren't comfortable seeing physical and mental illness on the same level. People committing suicide die of an illness in no different a way than people dying of cancer. Yet there is very little in the way of public support of combating suicide the way there is for cancer. There is little debate that opiates (dramatically more risk for abuse) should be used to treat physical pain, and yet people get very nervous about the potential for misuse in a much less risky drug which could provide similar relief to mental anguish.