I am not saying drugs can not make a person feel good. Of course they do. They can also cause depression too.
I hope that we can agree that drugs influence brain chemistry through various means; typically by influencing production, altering re-uptake, and directly binding to receptors.
It seems we agree that this can make a person feel good/bad.
What I don't agree with is telling a person the proof they are feeling bad is that they have a chemical problem even when they have no history of drug abuse.
Ahh, but "feeling" is analogous to "chemistry." Feeling either good or bad is directly related to brain chemistry. People start drinking and "feeling good." A relationship has "chemistry." This is exactly what a feeling is.
The difference between being sad and being depressed is clinical. If you are so sad for so long that it negatively interferes with your life for weeks, you are, by definition, "depressed." This can be completely natural, but is absolutely related to brain chemistry.
If someone loses a child, they may be understandably devastated emotionally for a long time. The act of crying actually releases hormones and other elements that effect brain chemistry:
Tears produced during emotional crying have a chemical composition which differs from other types of tears. They contain significantly greater quantities of the hormones prolactin, adrenocorticotropic hormone, Leu-enkephalin,[5] and the elements potassium and manganese.[3] Walter, Chip (December 2006). "Why do we cry?". Scientific American Mind 17 (6): 44. Skorucak A. "The Science of Tears."
The point I'm making is that everything you feel is intrinsically linked to brain chemistry. Logic and Emotion play important roles in our consciousness, and it is possible to "get your emotions under control" through natural means like crying and thinking "logically," it is also possible to cure mild depression through exercising (which naturally increases dopamine production) and through activating the reward system of the brain in other, healthy ways.
There is, however, a more severe form of depression that can stem from a natural, chemical imbalance in the brain. Most marketed anti-depressants are made to address depression that is not "natural." For example, being completely miserable all the time for no reason. You don't know why, you're just always sad; you know that there is no logical reason to be sad, but it doesn't matter, you're sad... all the time. You become suicidal, you don't socialize and it makes you more depressed which causes a feedback loop that just makes everything worse.
While I agree (and I'm sure most would), that these drugs are far from perfect, we don't currently understand enough about the problem to solve it. Current anti-depressants work by inhibiting serotonin (and in some cases norepinephrine) reuptake. This causes more of these chemicals to be available in the brain. How this makes you "feel" is subjective, but serotonin levels absolutely affect your mood.
Right now, you can basically take these drugs and either feel better or worse; it is better than no treatment at all, and while I agree that it's kind of like throwing a dart at a dartboard, it's better to try to fix what isn't working than to leave it alone. When it comes to treating depression, if you can get by without the medicine, that's good; if not, it's better than nothing.