> It can't be the use of reason [...] I don't think I have to explain why that would be a ridiculous position to take.
I think it would be better if you did, because otherwise you leave me guessing what your argument is, and if I guess wrong then I just wasted a lot of words for no good reason.
My guess is that you meant some combination of: "everyone is using their reason" and "everyone believes that their approach is the reasonable one" or "look at all those awesome scientists and philosophers, how many smart words they wrote and how many awesome inventions they made". Which is all true. But I wish I knew which one of these is closest to your objection, because they are not the same; the reason that everyone uses is obviously not the same degree or kind as the reason the awesome scientists use.
In my opinion, the thing that makes the rationality community different from everything else is a combination of things. None of these things, taken individually, is exclusive to the rationality community. Actually, most of the ideas, perhaps all of them, are taken from books written by someone else. The unique thing was (1) putting all these things together, (2) publicly, and (3) trying to take them seriously. As opposed to: only caring about one of these things and ignoring the rest, or teaching them only to selected people e.g. at school, or just discussing things without actually attempting to change your life because of them.
Here are some of the things:
* Probabilistic thinking. The idea that there is no absolute certainty, only probabilities. (Although some probabilities can, for all practical purposes, be very high or low.) That people should try to express their probabilities in numbers, and then calibrate themselves to get those numbers right. Getting probabilities right means that if you keep a log of all things that you have assigned to e.g. a 30% probability, then statistically about 30% of them should turn out to be true in long term. This was specifically taught at the rationality minicamps; they even made an app for that. Some math related to this.
* The consistency of reality. As opposed to e.g. the idea that science and religion are "separate magisteria" and each follows different laws of logic and probability. Nope. The laws of logic you use in your lab are exactly the same as the laws of logic you should use outside the lab. Just like gravity does not stop applying when your job is over, neither do the laws of evidence. Science is not a special world that plays by special rules; the atoms you study in the lab are the same atoms that the entire world is made of.
* People are "predictably irrational" (to use the popular phrase). Yes... and now that you know, you should do something about that. Even if you can't be perfect, that doesn't mean there is no low-hanging fruit to pick. Learn about the most frequent types of mistakes humans make, try to notice how it feels inside when you are doing that, and either try to avoid such situations, or try to recognize the feeling when it happens, or at least use some reflection to notice it afterwards. Together try to create an environment where those mistakes are easier to avoid.
* Notice the many ways how words can fail to reflect reality. For example, if you use the same word for two different things, it prevents you from noticing their differences. (But it is a natural mistake to make if those things are indeed similar, and if in the past they were interchangeable and just recently stopped being so.) How people incorrectly assume that everything that can be understood has a simple explanation, because that was kinda true in the jungle where our ancestors evolved. Etc.
* Reality matters. If your model of the world does not match reality, it is your model that is wrong. If you learn that fairies do not exist, that does not mean that the world suddenly became less magical -- it was always the same as now, only you didn't know it.
* Notice how you could do things better. Then actually do it.
* Ethics. Consequentialism and its problems. Good reasons to avoid temptations that seem convincing at the moment.
...and many more, sorry this already took too much time to write. If you are curious, https://www.readthesequences.com/ -- but the point is, this is not just about reading an interesting text, but actually changing yourself. And of course, there are many people who read the texts and don't change themselves. That cannot be prevented, especially when the text is freely available online. The rationality community actually had many workshops where people could practice these skills, so the opportunity was there.
Again, none of these things is scarce individually. It's the combination. For example, people who do math + care about improving the world = effective altruism. Trying to counter biases + caring about truth = steelmaning your opponents. Probabilistic thinking + reality matters = even if there is only 30% chance that a superhuman AI might kill us all, we better try hard to reduce that chance. The synergy of all of that... that is the goal that the rationality community is moving towards.