As a registered pharmacist that has struggled with depression (and refused medication as treatment for years while suffering, due to the shame) I know we have a long way to go. For one thing, we really don't know what we are diagnosing in many cases because most of the signs and symptoms are very subjective. There is no lab value to look at and say "this person is clearly recovered". There are no clear distinctions from one mental illness to another. As an example, autism and schizophrenia can overlap and cross each other in various ways while bipolar disorder type II can be confused with ADHD or simple depression or anxiety or a combination of all of the above in various ways. You can look at mental health as a ten dimensional spectrum (or far more) with endless points in between. There are definitely times when we can clearly say "this is major depressive disorder" or "this is bipolar type I" but overall, diagnosis is sort of a crap shoot. There ARE algorithms by which to diagnose, but these are also very subjective and not based on any specific physiological difference or structural difference.
As a result of this difficulty, medication can be a real educated guessing game. The lucky ones are able to find a single medication that helps (bupropion for myself). Others, such as those suffering with Bipolar I or Schizophrenia (two vastly varying diseases that can overlap) may search for an effective combination therapy for years. This is mostly because, as stated earlier, there are not perfect physiological markers to test for these diseases. We cannot correlate depression with serotonin levels in the body or the brain. We know that changing the balance of serotonin can help a person take a single step of many out of the cycle of depression, but we cannot treat to a specific serotonin level, as we would with a disease like diabetes. We can only move forward through examining the evidence that exists and make the best possible guess as to what will help.
I believe that our best hope lay within understanding the detailed circuitry of our brains as well as the genes that are most closely related to various mental illnesses. Until then, mental illness is likely to carry a stigma because some people will always think that depression is the same as being sad or having the blues. These people will always say "you just need to get over it" or "we all get sad sometimes". It's hard to explain the difference until you're actually experiencing it.
Having been diagnosed with severe depression, anxiety and PTSD, I believe that even though we have advanced in our opinions towards mental health, many people are still unaware of how serious it is. This is an issue that we must discuss, because each generation is getting more depressed as the stress levels increase.
Thanks to science and technology, no we are not still in the Dark Ages in relation to mental health. The crazy people (what they were referred to) were beaten, shocked, imprisoned, and even executed many times centuries ago. Today we have facilities, therapy, medication, intelligent diagnoses, and plenty more to help deal with mental health problems. More can be done, but we are far from the dark ages.
In the Dark Ages, mental health was not considered as much a health issue as it was a social/religious and economic issue. Those who were unfortunate to find themselves having emotional or mental issues, were shunned by even their own families, and found themselves sent away to sanitariums or prisons. If their family had money, they might find themselves locked away inside the family home and kept secret from outsiders. They were in fact not treated medically but treated with shame. Today the same conditions are unfortunately similar. A lack of understanding or information has allowed for too many people in need of help to go without it because of the embarrassment or inconvenience of other family members.
I believe society is still in the Dark Ages in relation to mental health. I believe the subject is still taboo is many respects where it shouldn't be. I believe we need to improve methods to treat mental illness and make it possible for suffers to integrate with society better.
No, society is not still in the Dark Ages in relation to mental health, because for the most part, people know about mental health and what it is today. There are people who will never be satisfied with the amount of attention and government funding that mental health treatment receives.