The idea is that you shouldn’t start your reasoning process from the conclusion, if you want to be rational. For a rational person, conclusion is what they get at the end, after weighing all available evidence, not a starting point.
Specifically, you don’t know whether “rationality would be beneficial for the society”. So you shouldn’t start at this point (the conclusion). What if you are wrong (but there is a selective evidence you could use to support your conclusion anyway)?
The idea is that you shouldn’t start your reasoning process from the conclusion, if you want to be rational. For a rational person, conclusion is what they get at the end, after weighing all available evidence, not a starting point.
Specifically, you don’t know whether “rationality would be beneficial for the society”. So you shouldn’t start at this point (the conclusion). What if you are wrong (but there is a selective evidence you could use to support your conclusion anyway)?