Vikarion, I'm not here to debate these issues with you. But really, as you don't want unjustifiable beliefs to affect society, why don't you go against the principle of induction - which has logically been shown to be unjustifiable - and on which all science rests? Also, scientism is no science, nor is metaphysical naturalism. I recommend to you to read up on the philosophy of science.
I'm using "unjustifiable" in the colloquial sense, here, not the formal logic sense. Obviously, there are axioms which must be held. However, when you were writing about spirituality, you were writing about it as in opposition to the "desolation" of atheism. When you write about "scientism", you wrote it in the context of arguing against the "tendency of people to place unjustified belief into the power of science to prognosticate and technically control.", with the correlation of "I think it misses some fundamental properties of reality that are important for the continued wellbeing of many (if not all) humans".
Now, there are, as I see it, two possible paths here. One is to argue that the current level of scientific knowledge is simply not sufficiently advanced to enable us to deal with some problems. This is certainly true. Yet, that doesn't seem to be what you assert. Rather, the second path here seems to be the one taken, that is, the belief that there are certain facets of human life and the universe which are fundamentally inaccessible to science.
Now, one might be forgiven for raising an eyebrow at the idea that a method of thinking which has proven so successful at producing results for the human race should be so utterly incompetent at eventually providing us results in some of the most important areas. Or, to put it more vividly, it seems a bit off to claim that science can produce the international space station, interplanetary probes, and my cell phone, but doesn't have anything truly useful or definitive to say about ethics, the human mind, or our religious beliefs.
Now, I did not assert metaphysical naturalism as necessarily true in and of itself. What I asserted was that if one believes that there are non-scientific forces at work in the world, then one is relegated to a much more untenable position regarding the reliability of science, including one's own observations. For such difficulties, I prefer Occam's Razor: it is better to conclude, absent contradictory evidence, that science is a valid and reliable guide to the universe than it is to conclude that there are any particular number of unverifiable, non-observable entities also involved in the universe.
Methodological naturalism does not necessarily, of course, rule out these entities. It is essentially just the assumption that one isn't dealing with supernatural entities at any particular point. But it is telling that we have not yet come across a situation where the presumption of naturalism has proven false. Again, Occam's Razor implores us to take the hint. Why should we multiply difficulties to ourselves?
I used to be a Christian. Our church had an interesting stance on depression, among other mental health issues: specifically, that they were essentially related to a spiritual world. Humans were sinners, they needed to be in fellowship with God, and if they resisted God or did not pursue a relationship (or a close enough relationship) with Him through His Son, they would suffer spiritually. These spiritual effects could manifest in physical ways, as well, from God punishing you with cancer, to you suffering from mental illness or depression.
This is an extraordinary theory, in that it, in my opinion, manages to be wrong twice. First, it creates enormously complicated causes for problems which may, in reality, be essentially simple. And it declares solutions to the problem that are probably too simple, and ineffective to boot. What my church ended up with, as a result, are some people who are nearly hysterical at times in their attempts to solve their problems with God. This is funny and stupid, I think, but probably not best for everyone.
Now, it's possible that they are right. Perhaps there is a God who you really do need a relationship with to live well. It could be. It could even be that this God is also not observable, testable, or verifiable. But Occam's Razor suggests that the simpler and cleaner scientific explanation is better: that the brain relies on certain chemicals to function well, and that when those chemicals get out of balance, problems can result, such as depression.
But if you ask my church, they'll tell you it's scientism to think that way, and that using drugs or psychology to treat mental issues is a sin.