Anti-depressants DO treat the cause! Because the cause is a chemical malfunction in your brain.
Actually, I believe any speak of "chemical imbalances" is still not a cause. It's likely an effect that is a result of many factors.
One solution that I think is good, but I don't think has been mentioned yet in this thread is diet. I don't just mean healthy servings of fruits and vegetables, or taking vitamins, but food sensitivities. You might be surprised how many people are affected by something like a gluten sensitivity, and how many of those people are depressed and feel better once they cut it out of their diet.
If you're really concerned about putting things in your body, perhaps it's time to consider what other things you are putting in your body. Because our brains very much work on chemicals. The food and drink that we consume can have an affect on that chemistry.
You say "our brains do work very much on chemicals" and then reject the idea that chemical imbalance can be the cause of mental illness? This makes no sense.