The Illness in question

I have a question to make not only for those that suffer with a mental disorder but also for the experts, if this is possible. I have noticed for a while now that SANE Australia uses the term “Mental Illness”.

I am just a normal person and I have Bipolar II. I don’t claim to be an expert, although I read a lot and have gone to university where I received two degrees, one in sociology and one in anthropology. I have also studied some clinical psychology and was encouraged to think independently and ask questions..

My question is this: if a condition such as Depression or Bipolar are an illness, then we are saying that we have identified the source of the Depression or Bipolar. By necessity an illness requires that the treating profession identifies the cause.

In cancer we identify the problem looking at cell tissue. In influenza we identify the variou bugs or viruses. But in mental illness where is the origin of the illness that causes the mind to become ill?

We cannot look at symptoms because symptoms are not the cause. Symptoms derive from the cause. We cannot say that it is genetic because for that we would also have to identify the exact problem that causes the genetic illness. And genes are expressed in the environment so how do we know if it is indeed genetic biology or genetic expression in the environment? No way to be certain. In the face of lack of evidence for a so called illness what to do?

Given that we have not identified the proper cause of the so called illness in mental problems, can we truly use this term? Are we correct using this term or are we misleading ourselves and the people?

I would appreciate an answer to my question, thank you. If an answer is not possible and not received I thank you anyway.