To be nitpicky...
We have such a negative impression of religion because we categorize anything irrational as "religion".
Being the least bit charitable, the irrational belief that the moon is made of cheese has nothing to do with religion and I am guessing most people here would not file it under that category. Your sentence might read better the other way:
We have such a negative impression of religion because we categorize anything "religious" as irrational.
At which point I would hazard that the community would accept it and wait for evidence to the contrary.
Consider Scientology [... et al]
I am not sure what you are asking us to consider.
Are you proposing these as examples of rational religions? I can follow the concept that a "rational religion" may or could exist, which is what I think you are trying to say, but I cannot tell if you think the religions you listed were rational.
Perhaps the list is an example of nontheistic religions? That seems to fit better with the rest of what you said:
[W]hy do we call these things religions? Because "religion", the way most non-LW people use it, has to do with providing explanations, perspectives, guidelines, and community
Providing explanations, perspectives, guidelines, and community fits a broader subject than "religions." Your average high-school fits those criteria and does not qualify as a religion. At this point it would also be useful to start trying to strictly define the terms. This is especially true if you think that "religion" is negatively and unfairly associated with "irrational."
Unless you explicitly point out that you're not talking about religion in general, I would expect the majority of LW readers to classify this mentally in the "arguments against religion" folder.
Personally, I drop it in the folder labeled "arguments related to religion." Argue semantics all you want, it fits.
The religions I listed, some of which are theistic, do not claim to be immune to evidential reasoning. The post says that is the defining characteristic of religion.
There's a reason we can all agree on theism as a good source of examples of irrationality.
Let's divide the factors that lead to memetic success into two classes: those based on corresponding to evidence, and those detached from evidence. If we imagine a two-dimensional scattergram of memes rated against these two criteria, we can define a frontier of maximum success, along which any idea can only gain in one criterion by losing on the other. This doesn't imply that evidential and non-evidential success are opposed in general; just that whatever shape memespace has, it will have a convex hull that can be drawn across this border.
Religion is what you get when you push totally for non-evidential memetic success. All ties to reality are essentially cut. As a result, all the other dials can be pushed up to 11. God is not just wise, nice, and powerful - he is all knowing, omnibenificent, and omnipotent. Heaven and Hell are not just pleasant and unpleasant places you can spend a long time in - they are the very best possible and the very worst possible experiences, and for all eternity. Religion doesn't just make people better; it is the sole source of morality. And so on; because all of these things happen "offstage", there's no contradictory evidence when you turn the dials up, so of course they'll end up on the highest settings.
This freedom is theism's defining characteristic. Even the most stupid pseudoscience is to some extent about "evidence": people wouldn't believe in it if they didn't think they had evidence for it, though we now understand the cognitive biases and other effects that lead them to think so. That's why there are no homeopathic cures for amputation.
I agree with other commentators that the drug war is the other real world idea that I would attack here without fear of contradiction, but I would still say that drug prohibition is a model of sanity compared to theism. Theism really is the maddest thing you can believe without being considered mad.
Footnote: This was originally a comment on The uniquely awful example of theism, but I was encouraged to make a top-level post from it. I should point out that there are issues with my dividing line between "evidence-based" and "not evidence-based", since you could argue that mathematics is not evidence-based and nor is the belief that evidence is a good way to learn about the world; however, it should be clear that neither of these has the freedom that religion has to make up whatever will make people most likely to spread the word.