It is an empirical truth that people tend to become more like what they pretend to be.

You can't pretend to agree with a counter-rational position, or believe in counter-rational arguments, without degrading your own rationality. Whether it's theoretically possible for minds to exist such that this does not occur doesn't matter. Our minds are structured so that it does.

Furthermore, I am highly skeptical of the position that despite valuing rationality enough to stick to it even in the face of inconvenience and countermotivations, rationalists could plausibly value the inaccuracy of people they supposedly care about.