this is a question of apriori not empirical facts....
Metaphysics is ontology and epistemology, not morality. Biology has nothing to do with truth.
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I think they (progress) will be achieved from a framework of theism, but in a slow way, that will leave behind piece by piece the spiritualism from theism, until it is reduced to the pure belief of transcendent perfection without content. That kind of theism would be compatible with nihilism and the two could coexists as mutually agnostic. The problem is that traditional theism brings spiritualism, and that spiritualism is just a more primitive type of thought, and that its bad when applied to knowledge, or morality. For example its hard to understand and artificially reconstruct the mind, if people think its an eternal substance completely separate from matter. Basically, I don't really care what anyone believes, as long as it doesn't determine knowledge, but because spiritualism practically always does, I'm against it.
Nihilnegativum we agree that this is a question of apriori knowledge the base fundamental assumptions about that nature of reality. Arguments on eventual convergence aside nihilism and theism represent competing and mutually exclusive views on reality. How should a rational individual choose between competing apriori assumptions?
One approach is to adopt the position that most appeals to the self as true and accept it as true regardless of the secondary cascade of consequences that result. This approach might lead one to choose either theism or nihilism.
A more practical approach is to examine the results of the choice and use that additional information to help guide the choice. Your concerns regarding the suppression of knowledge by spiritualism are valid based on historical president. However, my concerns regarding the undermining of health, well-being, and social stability by nihilism are also valid based on current data. By your own admission and logic you expect spiritualism to fade away with time leaving a theism of transcendent perfection that is entirely compatible with knowledge. I have no similar expectations regarding the detrimental effects of nihilism.
One can argue that biological, moral, and anthropological arguments are entirely irrelevant in a discussion of metaphysics but this conclusion too stems from apriori assumptions. It is hard, usually impossible, to induce a re-examination of fundamental assumptions. However, what you currently regard as 'truth' is essentially choice and dictated by assumptions, which are not compelled. Looked at this way, to choose modern nihilism rather than the natural, spontaneous, 'biological' tendency to religious explanations is not just foolish, but incoherent - since the choice of nihilistic assumptions makes that choice itself meaningless.