It lets us know right away when an idea is wrong. Religion is not just wrong, but uniquely wrong. It is always wrong.
How seriously do you want to support this claim?
I mean, among the most famous claims of several popular American religions is that "Don't murder" and "Don't steal" are important moral principles. I will admit to being more than a little partial to those principles myself. If I take your claim literally it follows that I should reject those principles.
If you're just engaging in hyperbole and don't really mean what you wrote, that's fine; please don't feel obligated to defend it just for consistency's sake. But if you do mean it, I'm interested in your more detailed reasoning.
The basis for the idea of "Thou Shalt Not Murder" is not religious. Before the commands, there was Hammurabi's Code, and before that Sumerian Code of Ur-Nammu, and before that it was custom. The earliest laws were a codification of what people were already doing. In other words, if Scientology claims they had invented calculus, that doesn't mean I suddenly distrust my ability to do derivatives.
A cleaner definition would be that 'supernatural explanations are always wrong', of which religious explanations are a subset. If I were to go into ful...
I've recently run across this 2007 post on the blog Unqualified Reservations (archive best read here). It is written by Mencious Moldbug, who is probably familiar to some Overcoming Bias and Lesswrong readers. He is a erudite, controversial and most of all contrarian social critic and writer. In 2010 he debated Robin Hanson on the subject of Futarchy.
Violating Godwin's law to breach the fence between religion and ideology to see what cognitive dissonances we can dredge up is old hat for us LWers (A Parable On Obsolete Ideologies 2009 by Yvain).
I hope you can now see reason I've picked a partially misleading title, since I think Moldbug makes a pretty convincing argument that belief in "religion" may be considered harmful even for atheists, let alone those of us who aspire to refine rationality.
In such a model questions like "is the Church of Scientology a religion?" dissolve rapidly. Whether something should be tax exempt because it is "really" a "religion" or "a church" is a legal question of importance only to activists trying to challenge law and lawyers, that shouldn't change our ethical intuitions or cause us to try to imagine a sea or play up rather minor geographical features, to separate the continents of Religion and Ideology in our maps of reality.
Every single proposed mechanism for the retention and spread of religion from convenient curiosity stoppers, indoctrination of youth, to tribal identity markers hold for ideology just as strongly as for religion. Even seemingly very specific memetic adaptations like "God of the gaps", seem to arise in various non-theistic ideologies. Maybe similar adaptations arise because it is the same niche?
Thinking about the implications of such a hypothesis, atheism for one additional god is a rather easy step of rationality to take. Very few people believe in the great Juju or Zeus. Adding YHWH to the list isn't that much of a stretch, for those fortunate enough to be educated and living in most of the West.
But how hard is it for someone to question, in a unbiased fashion, such gods and holy words such as say Democracy?