I've argued rather extensively against religion on this website.
That was my impression as well, but when I went looking for those arguments, they were very difficult to find. Perhaps my Google-fu is weak. Help from LW readers is welcome.
I found plenty of places where you spoke disrespectfully about religion, and quite a few places where you cast theists as the villains in your negative examples of rationality (a few arguably straw-men, but mostly fair). But I was surprised that I found very few places where you were actually arguing against religion.
Name a single one of those arguments which is equally effective against simulationism.
Well, the only really clear-cut example of a posting-length argument against religion is based on the "argument from evil". As such, it is clearly not equally effective against simulationism.
You did make a posting attempting to define the term "supernatural" in a way that struck me as a kind of special pleading tailored to exclude simulationism from the criticism that theism receives as a result of that definition.
This posting rejects the supernatural by defining it as 'a belief in an explanatory entity which is fundamentally, ontologically mental'. And why is that definition so damning to the supernaturalist program? Well, as I understand it, it is because, by this definition, to believe in the supernatural is anti-reductionist, and a failure of reductionism is simply inconceivable.
I wonder why there is not such a visceral negative reaction to explanatory entities which are fundamentally, ontologically computational? Certainly it is not because we know of at least one reduction of computation. We also know of (or expect to someday know of) at least one reduction of mind.
But even though we can reduce computation, that doesn't mean we have to reduce it. Respectable people have proposed to explain this universe as fundamentally a computational entity. Tegmark does something similar, speculating that the entire multiverse is essentially a Platonic mathematical structure. So, what justification exists to deprecate a cosmology based on a fundamental mental entity?
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I only found one small item clearly supporting my claim. Eliezer, in a comment, makes this argument against creationists who invoke the Omphalos hypothesis
Never mind usefulness, it seems to me that "Evolution by natural selection occurs" and "God made the world and everything in it, but did so in such a way as to make it look exactly as if evolution by natural selection occured" are not the same hypothesis, that one of them is true and one of them is false, that it is simplicity that leads us to say which is which, and that we do, indeed, prefer the simpler of two theories that make the same predictions, rather than calling them the same theory.
I agree. But take a look at this famous paper by Bostrom. It cleverly sidesteps the objection that simulating an entire universe might be impossibly difficult by instead postulating a simulation of just enough physical detail so as to make it look exactly as if there were a real universe out there. "Are you living in a computer simulation?" "Are we living in a world which only looks like it evolved?" Eliezer chose to post a comment answering the latter question with a no. He has not, so far as I know, done the same with Bostrom's simulationist speculation.
I found plenty of places where you spoke disrespectfully about religion, and quite a few places where you cast theists as the villains in your negative examples of rationality (a few arguably straw-men, but mostly fair). But I was surprised that I found very few places where you were actually arguing against religion.
The post you are looking for is Religion's Claim to be Non-Disprovable
Many folk here on LW take the simulation argument (in its more general forms) seriously. Many others take Singularitarianism1 seriously. Still others take Tegmark cosmology (and related big universe hypotheses) seriously. But then I see them proceed to self-describe as atheist (instead of omnitheist, theist, deist, having a predictive distribution over states of religious belief, et cetera), and many tend to be overtly dismissive of theism. Is this signalling cultural affiliation, an attempt to communicate a point estimate, or what?
I am especially confused that the theism/atheism debate is considered a closed question on Less Wrong. Eliezer's reformulations of the Problem of Evil in terms of Fun Theory provided a fresh look at theodicy, but I do not find those arguments conclusive. A look at Luke Muehlhauser's blog surprised me; the arguments against theism are just not nearly as convincing as I'd been brought up to believe2, nor nearly convincing enough to cause what I saw as massive overconfidence on the part of most atheists, aspiring rationalists or no.
It may be that theism is in the class of hypotheses that we have yet to develop a strong enough practice of rationality to handle, even if the hypothesis has non-negligible probability given our best understanding of the evidence. We are becoming adept at wielding Occam's razor, but it may be that we are still too foolhardy to wield Solomonoff's lightsaber Tegmark's Black Blade of Disaster without chopping off our own arm. The literature on cognitive biases gives us every reason to believe we are poorly equipped to reason about infinite cosmology, decision theory, the motives of superintelligences, or our place in the universe.
Due to these considerations, it is unclear if we should go ahead doing the equivalent of philosoraptorizing amidst these poorly asked questions so far outside the realm of science. This is not the sort of domain where one should tread if one is feeling insecure in one's sanity, and it is possible that no one should tread here. Human philosophers are probably not as good at philosophy as hypothetical Friendly AI philosophers (though we've seen in the cases of decision theory and utility functions that not everything can be left for the AI to solve). I don't want to stress your epistemology too much, since it's not like your immortal soul3 matters very much. Does it?
Added: By theism I do not mean the hypothesis that Jehovah created the universe. (Well, mostly.) I am talking about the possibility of agenty processes in general creating this universe, as opposed to impersonal math-like processes like cosmological natural selection.
Added: The answer to the question raised by the post is "Yes, theism is wrong, and we don't have good words for the thing that looks a lot like theism but has less unfortunate connotations, but we do know that calling it theism would be stupid." As to whether this universe gets most of its reality fluid from agenty creators... perhaps we will come back to that argument on a day with less distracting terminology on the table.
1 Of either the 'AI-go-FOOM' or 'someday we'll be able to do lots of brain emulations' variety.
2 I was never a theist, and only recently began to question some old assumptions about the likelihood of various Creators. This perhaps either lends credibility to my interest, or lends credibility to the idea that I'm insane.
3 Or the set of things that would have been translated to Archimedes by the Chronophone as the equivalent of an immortal soul (id est, whatever concept ends up being actually significant).